THE  LIBRARY 

OF 

THE  UNIVERSITY 
OF  CALIFORNIA 


PRESENTED  BY 

PROF.  CHARLES  A.  KOFOID  AND 
MRS.  PRUDENCE  W.  KOFOID 


THE  "SHOWN  TO  THE  CHILDREN"  SERIES 
EDITED  BY  LOUEY  CHISHOLM 


THE  MICROSCOPE 


The 
44  Shown  to  the  Children  "  Scries 

i.  BEASTS. 

With  48  Coloured  Plates  by  PERCY  J.   BILLING- 
HURST.     Letterpress  by  LENA  DALKEITH. 
a.  FLpWERS. 

With  48  Coloured  Plates  showing  1 50  flowers,  by  J  ANET 
HARVEY  KELMAN.     Letterpress  by  C.  E.  SMITH. 

3.  BIRDS. 

With    48  Coloured    Plates    by  M.   K.   C.   SCOTT. 
Letterpress  by  J.  A.  HENDERSON. 

4.  THE  SEA-SHORE. 

With  48  Coloured  Plates  by  JANET  HARVEY  KELMAN. 
Letterpress  by  Rev.  THEODORE  WOOD. 

5.  THE  FARM. 

With  48  Coloured  Plates  by  F.  M.  B.  and  A.  H. 
BLAIKIB.     Letterpress  by  FOSTER  MEADOW. 

6.  TREES. 

With  32  Coloured  Plates  by  JANET  HARVEY  KELMAN. 
Letterpress  by  C.  E.  SMITH. 

7.  NESTS  AND  EGGS. 

With  48  Coloured  Plates  by  A.  H.  BLAIKIE.    Letter- 
press by  J.  A.  HENDERSON. 

8.  BUTTERFLIES  AND   MOTHS. 

With  48  Coloured  Plates  by  JANET  HARVEY  KELMAN. 
Letterpress  by  Rev.  THEODORE  WOOD. 

9.  STARS. 

By  ELLISON  HAWKS. 

10.  GARDENS. 

With  32  Coloured  Plates  by  J.  H.  KELMAN.    Letter- 
press by  J.  A.  HENDERSON. 

xi.  BEES. 

By  ELLISON   HAWKS.     Illustrated  in  Colour  and 
Black  and  White. 

«.  ARCHITECTURE. 

By  GLADYS  WYNNE.    Profusely  Illustrated. 

13.  THE  EARTH. 

By  ELLISON  HAWKS.     Profusely  Illustrated. 

14.  THE  NAVY. 

By  PERCIVAL  A.  HISLAM.    48  Two-colour  Plates. 

15.  THE  ARMY. 

By  A.  H.  ATTERIDGE.   16  Colour  and  32  Black  Plates. 

16.  WORK  AND   WORKERS. 

By  ARTHUR  O.  COOKE.    48  Illustrations. 

17.  THE  MICROSCOPE. 

By  ELLISON    HAWKS.     Illustrated  in  Colour  and 
Black  and  White. 


drawing  by 


Volvox 


[G.  Fisher-Jones 


The  Microscope 


BY 

CAPTAIN   ELLISON   HAWKS 

Author  of  "Stars,"  "Bees,"  "The  Earth,"  Shown  to  the  Children 

"The  Boy's  Book  of  Astronomy,"  "The  Romance  of  Water 

in  Nature,"  etc.;  and  Editor  of  Messrs.  Jack's 

"Romance  of  Reality"  Series 


THOMAS   NELSON   AND   SONS 

NEW    YORK 


TO 
MY   YOUNG   FRIEND 

JOHN 

THIS   BOOK   IS   AFFECTIONATELY 
DEDICATED 


CONTENTS. 

I   THE  STORY  OF  THE  MICROSCOPE         .      .  n 

II.  THE  PRINCIPLE  OF  THE  COMPOUND  MICRO- 
SCOPE   .      .             .             .       .  16 

III.  WORKING  WITH  THE  MICROSCOPE         . '     .  30 

IV.  MICROSCOPIC  PLANTS       .      . .     .      .      .  40 

V.  MICROSCOPIC  ANIMALS     .       .      .      .      .  53 

VI.  DAPHNIA  AND  CYCLOPS  .      .      .      .      «  65 

VII.  PLANT  LIFE      .      .      .      .      ...  73 

VIII.  FLOWERS V.  87 

IX.  FUNGI  AND  MOULDS        .....  95 

X.  MARINE  LIFE     .       .      .      .      .       .      .  104 

XL  AN  INSECT  LABORATORY  AND  WORKSHOP  : 

THE  HONEY-BEE       .      .       .       ;       .  115 

XII.  OTHER  INSECTS        .      .      .       .      »      *  130 

XIII.  MINIATURE  ENGINEERS  :  SPIDERS       .      i  147 


ABOUT  THIS   BOOK. 

DEAR  JOHN, 

Many  years  ago  I  remember  reading  a  fairy 
tale  called,  I  think,  The  Rose-Coloured  Spectacles.  It 
told  of  a  wonderful  pair  of  spectacles  which  caused 
everything  to  appear  different  to  the  person  who  was 
wearing  them.  Things  looked  so  very  changed  as  seen 
through  these  rose-coloured  spectacles  and  so  many 
new  features  were  discerned,  that  people  came  from  far 
and  wide  to  look  through  them. 

Unfortunately  the  secret  of  the  manufacture  of  the 
rose-coloured  spectacles  has  never  been  discovered. 
An  instrument  has  been  made,  however,  which  nearly 
approaches  them,  and  actually  surpasses  them  in  the 
wonderful  things  it  shows.  This  instrument  is  the 
Microscope,  and  in  this  little  book  I  shall  endeavour 
to  help  you  to  look  through  it  and  to  see  some  of  the 
wonderful  things  it  reveals  in  the  great  realm  of  Nature. 

Almost  any  object,  no  matter  how  commonplace,  will 
show  new  features  of  interest  when  magnified.  You  will 
readily  understand,  therefore,  that  in  this  little  book 
I  cannot  attempt  to  tell  you  how  everything  looks,  as 
seen  with  the  microscope — in  fact,  no  one  could  write 

(2,084)  9  2 


io  ABOUT  THIS   BOOK. 

such  a  book.  There  are  so  many  interesting  objects  tc 
write  about,  indeed,  that  it  has  been  difficult  for  me  to 
decide  what  was  to  be  included  and  what  was  to  be  left 
out.  I  felt,  however,  that  you  would  like  most  of  all 
to  hear  of  what  the  microscope  reveals  in  objects  of 
everyday  interest ;  that  you  want  to  know  what  such 
things  as  pollen  and  plant  cells  look  like,  and  to  learn 
exactly  by  what  means  a  spider  spins  its  web  and  a  bee 
stings.  Therefore,  practically  all  the  objects  I  have 
described  are  such  as  any  one  may  see  if  he  or  she  be 
the  fortunate  possessor  of  a  microscope — even  though 
it  may  not  be  a  very  powerful  one.  Not  only  may  you 
see  these  objects,  but  from  the  little  I  have  told  you 
about  them,  you  will  be  able  to  understand  them,  to 
know  something  of  their  life-history  and  of  the  part 
they  play  in  Nature. 

I  feel  sure  you  will  join  me  in  giving  thanks  to 
my  friends  who  have  kindly  assisted  me  with  some  of 
the  illustrations.  To  Mr.  G.  Fisher-Jones,  F.R.M.S., 
for  the  very  beautiful  coloured  plates  so  accurately  and 
artistically  drawn.  To  Mr.  Chas.  D.  Holmes,  Mr.  A.  E. 
Smith,  Mr.  E.  A.  Pinchin,  Mr.  W.  Brough-Randles,  B.Sc., 
Mr.  W.  Coles-Finch,  Mr.  J.  Holmes ;  and  to  Messrs. 
Flatters,  Ltd.,  and  to  Messrs.  Pathe  Freres.  My  in- 
debtedness to  Captain  W.  R.  Booth  and  Mr.  Chas.  D. 
Holmes  for  reading  over  the  proofs  must  also  be 
mentioned. 

Yours  truly, 

ELLISON  HAWKS. 

io  GRANGE  TERRACE,  LEEDS, 
November  1919. 


THE    MICROSCOPE. 

CHAPTER  I. 
THE  STORY  OF  THE  MICROSCOPE. 

I. 

THE  microscope  derives  its  name  from  two  Greek 
words,  mikros,  "  small,"  and  skopeo,  "  to  see  or 
observe."  A  microscope  presents  to  the  eye  of  its  user  a 
magnified  image  of  the  object  under  examination.  The 
simplest  form  of  microscope  is  an  ordinary  lens,  such  as  a 
reading  glass  or  pocket  magnifier.  With  the  help  of  a  low- 
powered  microscope  we  are  able  to  magnify  objects  so 
that  there  become  visible  details  which  cannot  be  seen 
with  the  naked  eye.  By  means  of  a  more  powerful 
instrument  we  are  able  to  see  objects  which  are  other- 
wise quite  invisible,  and  of  the  existence  of  which  we 
should  probably  remain  in  complete  ignorance  but  for 
the  microscope. 

The  microscope  may  thus  be  likened  to  a  window 
through  which  we  are  able  to  look  upon  a  new  and 
wonderful  Fairyland.  Here  objects  measuring  no  more 

than  a  quarter  of  a  millionth  part  of  an  inch  in  size  are 

11 


12  THE  MICROSCOPE. 

revealed  to  us,  and  made  to  record  themselves  on  the 
photographic  plate.  A  drop  of  water  from  a  pond  may 
be  so  magnified  that  we  find  it  is  almost  a  world  in  itself, 
containing  specimens  of  minute  vegetable  and  animal 
life.  The  very  construction  and  origin  of  these  minute 
forms  of  life  are  often  such  as  to  present  to  us  the  most 
difficult  problems,  which  even  our  cleverest  scientists 
and  chemists  are  unable  to  successfully  and  completely 
solve. 

Again,  a  pinch  of  knife  polish  may  contain  microscopic 
shells,  which  are  really  the  skeletons  of  minute  creatures 
which  lived  ages  ago.  These  shells  are  so  delicate  and 
beautiful  in  appearance  that  our  greatest  artists  would 
gladly  use  them  as  patterns  for  designs  if  they  could. 
So  I  might  go  on,  pointing  out  to  you  the  wonders  which 
the  invention  of  the  microscope  has  laid  bare  to  the  gaze 
of  all  who  care  to  look. 

II. 

The  actual  date  of  the  invention  of  the  microscope 
and  the  name  of  its  inventor  are  unknown.  It  has  been 
said  that  magnifying  glasses  were  known  to  the  ancient 
Egyptians,  but  whether  this  was  so  or  not  now  appears 
uncertain.  In  the  first  century,  Seneca — the  tutor  of 
the  infamous  Roman  Emperor  Nero — noticed  that  if  a 
globe  of  glass  be  filled  with  water,  writing  seen  through 
it  appeared  larger  than  it  really  was.  Galen,  the  learned 
Greek  physician,  tells  us  definitely  that  magnifying 
glasses  were  certainly  not  known  to  the  Greeks  and 
Romans  in  the  first  and  second  centuries.  Much  later — 
in  the  eleventh  century — the  Arabians  seemed  to  have 


PLATE    II 


From  a  water-colour  drawing  by]  [G.  Fisher-Jones 

1.   Desmida 

(a)  Arthrodesm-us,  (l>)  Closteriutn,  (c)  Desmidium,  (d)  Euasirnm,  (e)  Pediastritin, 
(/)  Scenedesiiius,  (^-)  Tetaieniorus,  (/i)  Xantliidium. 

2.     Stages    of    division    of    a    Desmid 
Afic.rasterias,  forming  two  individuals. 


ROGER  BACON.  13 

known  and  used  some  form  of  magnifying  glass.  Beyond 
these  few  facts  nothing  of  importance  has  been  discovered 
of  any  early  evidences  of  magnifying  glasses,  and  until 
the  thirteenth  century  very  little  appears  to  have  been 
known  about  them. 

In  1276,  however,  Roger  Bacon — a  Franciscan  monk 
of  Ilchester  —  presented  his  Opus  Majus  to  Pope 
Clement  IV.  In  this  interesting  volume  Roger  Bacon 
showed  how  crystal  lenses  could  be  used  to  make  objects 
appear  larger.  "  With  these  lenses,"  he  said,  "  an  instru- 
ment could  be  made,  useful  to  old  men  and  to  those  whose 
sight  is  weakened,  for  by  means  of  it  they  would  be  able 
to  see  letters,  however  small  they  are,  made  large  and 
clear.  .  .  ." 

In  the  days  when  Roger  Bacon  lived  people  did  not 
understand  science  as  we  do  to-day,  believing  in  sorcery 
and  witchcraft.  They  thought  that  any  one  who  had 
discovered  lenses  such  as  those  described  by  Roger 
Bacon  must  indeed  have  gone  to  the  devil  himself  for 
assistance  !  It  was  ordered,  therefore,  that  he  should  be 
cast  into  prison.  His  Opus  Majus  was  hidden  away — 
perhaps  by  some  of  his  friends,  but  this  we  do  not  know 
— and  remained  lost  until  discovered  in  1733,  nearly  five 
hundred  years  later.  By  this  time  a  form  of  microscope 
had  been  in  use  for  over  one  hundred  years,  and  Roger 
Bacon  was  thus  robbed  of  the  credit  of  the  discovery, 
as  well  as,  perhaps,  of  the  discovery  of  the  telescope. 

Many  careful  investigations  have  been  made  in  the 
attempt  to  find  who  constructed  the  first  microscope. 
It  is  now  believed  that  it  was  made  at  some  date  between 
1590  and  1609,  and  that  the  credit  for  the  invention 


14  THE  MICROSCOPE. 

must  be  given  to  one  of  three  spectacle  makers  of  Middel- 
burg  in  Holland — Hans  Janssen,  his  son  Zacharias,  or 
Hans  Lippershey. 

One  of  the  earliest  accounts  of  the  microscope  and  of 
observations  with  the  instrument  was  given  in  1665,  by 
the  celebrated  Dr.  Robert  Hooke.  It  was  published 
in  a  large  volume  called  Micrographia,  a  copy  of  which 
is  to  be  seen  in  the  British  Museum.  Dr.  Hooke 
describes  his  microscope  as  having  a  tube :  "...  for 
the  most  part  not  above  six  or  seven  inches  long,  though 
by  reason  that  it  had  four  drawers  it  could  easily  be 
lengthened  as  occasion  required.  .  .  ." 

We  shall  shortly  learn  that  microscopes  are  of  two 
kinds,  called  simple  and  compound.  The  instrument 
used  by  Dr.  Hooke  was  of  the  compound  type,  and  is  the 
same  in  principle  as  most  of  the  microscopes  of  the 
present  day. 

Some  few  years  after  Dr.  Hooke  published  his  Micro- 
graphia  another  worker,  named  Leeuwenhoek,  made  a 
simple  microscope,  and  in  1673  communicated  some 
of  his  discoveries  to  the  Royal  Society.  He  did  not 
describe  his  instrument,  however,  but  when  he  died  he 
left  to  the  Royal  Society  a  cabinet  containing  twenty-six 
of  his  microscopes.  His  work  is  of  importance  because 
it  then  came  to  be  believed  that  the  form  of  microscope 
he  used — that  is,  the  simple  type — was  better  than  the 
compound  type  advocated  by  Dr.  Hooke.  Because  of 
Leeuwenhoek's  work  the  compound  microscope  fell  into 
disrepute,  and  no  improvements  in  it  were  effected  for  a 
considerable  time. 


BENJAMIN  MARTIN.  15 

To  Benjamin  Martin  is  due  the  credit  for  many  advances 
on  the  earlier  models.  In  1742  he  made  an  ingenious 
microscope  and  gave  it  to  George  III.,  and  this  instru- 
ment is  now  in  the  possession  of  the  Royal  Microscopical 
Society.  It  was,  perhaps,  the  best  microscope  of  any 
made  up  to  that  time.  Professor  Quekett,  a  well-known 
microscopist,  has  described  it,  saying  that  it  is  about 
two  feet  high,  and  is  supported  on  a  tripod  base.  The 
body,  three  inches  in  diameter,  is  composed  of  two  tubes, 
which  can  be  raised  or  lowered.  There  are  twenty-four 
lenses,  and  these  have  been  very  carefully  constructed. 

Martin  was  quickly  followed  by  numerous  other  workers, 
and  during  the  ensuing  years  the  microscope  rapidly 
developed.  These  early  microscopes  were  very  crude 
and  imperfect,  and  were  you  able  to  see  one  you  would 
probably  be  very  puzzled  to  know  what  kind  of  an 
instrument  it  could  be,  even  though  you  knew  what  a 
modern  microscope  looks  like.  As  time  went  on,  how- 
ever, and  the  manufacture  of  glass  lenses  gradually 
became  more  perfect,  microscopists  were  able  to  improve 
on  the  early  ideas,  and  little  by  little  the  wonderful 
microscope  of  to-day  was  perfected. 

The  microscope  may  be  said  to  be  one  of  our  most 
recent  instruments,  for  its  true  principles  were  not 
generally  known  until  about  1881. 


CHAPTER  II. 

THE  PRINCIPLE  OF  THE  COMPOUND 
MICROSCOPE. 

I. 

THE  microscope — or  indeed  any  magnifying  glass — 
acts  in  the  same  way  as  the  crystalline  lens  of  our 
eyes  and  depends  upon  refraction.  Refraction  may  be 
thus  explained.  When  a  ray  of  light  passes  through 
one  substance — or  medium,  as  it  is  called — into  another 
of  different  density,  the  path  of  the  ray  is  bent  or  re- 
fracted. Thus,  a  ray  of  light  passing  from  air  into  water 
is  refracted,  because  water  is  of  different  density  to  air. 
This  may  be  clearly  seen  by  putting  a  pencil  or  other 
object  into  a  basin  of  water.  The  pencil  appears  to 
be  bent  or  broken  at  the  point  where  it  enters  the  water 
(see  a,  Fig.  i).  Why  this  should  be  so  is  shown  in 
b,  Fig.  i,  where  we  see  indicated  the  path  of  a  ray  of  light 
coming  from  the  end  of  the  pencil  to  the  eye.  At  the 
point  where  the  ray  comes  out  of  the  water  it  is  bent ; 
but  the  eye  does  not  see  this,  and  instead  of  our  being 
able  to  perceive  the  true  position  of  the  end  of  the  pencil, 
we  seem  to  see  it  lying  on  an  imaginary  line.  A  ray  of 
light  passing  through  a  lens  is  refracted  in  a  similar 

16 


PLATE  III 


From  photo-micrographs  by] 


[E.  Cuzner,  F.R.M.S. 


DISC-SHAPED    DIATOMS 
(a)  Craspedodiscus.       (b)  Heliopelta 


REFRACTION.  17 

manner,  the  amount  of  the  refraction  depending  upon 
the  nature  and  curvature  of  the  lens. 

Seneca  did  not  try  to  understand  why  writing  looked 
larger  through  a  glass  globe  filled  with  water.    Had  he 


&y 

FIG.  i. — Experiment  to  illustrate  refraction  of  rays. 

done  so  he  would  have  discovered  that  the  curved  surface 
of  a  globe  bends  inward  the  rays  of  light,  because  glass 
and  water  are  more  dense  than  air.  It  was  by  using  this 
principle  that  the  microscope  was  thought  of. 

A  lens  refracts  the  rays  from  the  object  under  examina- 
tion to  an  eyepiece,  and  it  is  here  that  the  eye  is  placed. 
The  point  at  which  the  rays  from  the  lens  gather  is 
called  the  focus.  At  this  point  is  formed  an  image  of 
the  object,  and  this  is  magnified  by  the  eyepiece. 

The  principle  may  be  explained  in  a  rough  way  by 
comparing  the  lens  to  a  funnel  placed  in  a  bottle.  If  placed 
in  the  rain  the  bottle  is  filled  more  quickly  than  would 
be  the  case  if  no  funnel  were  used.  A  lens  collects  not 
raindrops  but  rays  of  light,  and  directs  them  to  the  eye 
of  the  observer  (Fig.  2).  By  these  means  the  eye  is 

(2,084)  3 


18  THE  MICROSCOPE. 

enabled  to  grasp  more  rays  than  it  would  do  if  a  lens 
were  not  used — in  other  words,  the  object  appears  mag- 
nified. 

The  same  principle  is  the  basis  of  opera-glasses,  tele- 


lens 


FIG.  2.  —  Lens  collecting  rays  of  light. 

scopes,  and  spectacles.  The  latter  were  at  first  (about 
1285)  called  "  magic  glasses,"  because  the  ignorant  people 
did  not  know  of  the  simple  principle  upon  which  they 
are  based. 

II. 

I  have  already  mentioned  that  microscopes  are  of  two 
kinds,  simple  and  compound.  A  simple  microscope  con- 
sists of  a  single  lens,  or  sometimes  of  two  such  lenses 
placed  close  together.  It  will  magnify  an  object  ten  or 


(a)  XX        "-    (I/) 

FIG.  3. — Pocket  lenses. 


(c) 


twenty  times.  Simple  microscopes  are  in  everyday  use 
as  reading  glasses  and  similar  appliances.  A  more  com- 
pact form  is  the  pocket  lens,  three  types  of  which  are 
shown  in  Fig.  3.  The  form  which  is  most  useful  is  that 
shown  at  b,  being  fitted  with  three  lenses  and  a  "  stop," 


THE  COMPOUND  MICROSCOPE.  19 

or  small  hole,  which  enables  a  clearer  image  to  be  obtained. 
Different  magnifications  may  be  obtained  by  using  the 
various  lenses  separately,  and  still  greater  magnification 
is  possible  by  using  a  combination  of  two  or  of  all  three 
lenses.  Leeuwenhoek's  microscope  was  an  improvement 


Eye  Lens 


Field  Lens 

T, 

r    ~\  [ 

«>l 

BodgTube  ... 
Draw  Tube 

i 

!l 

S&.  ~flM 

Exje  Piece 


JDrmu  Tube 


Objective 
Cover  Glaff 


Glass  Slide 
FIG.  4. — Section  of  a  microscope  showing  the  principal  parts. 

on  a  simple  lens,  for  sometimes  it  magnified  the  object 
under  examination  270  times. 

The  compound  microscope,  in  which  we  are  more  par- 
ticularly interested,  consists  of  two  sets  of  lenses  (Fig.  4). 
The  first  set  is  placed  at  that  end  of  the  tube  which  is 
nearest  the  object  to  be  examined,  and  is  therefore  called 


20  THE  MICROSCOPE. 

the  "  objective."  The  second  set  of  lenses  is  situated 
at  the  other  end  of  the  tube  and  is  called  the  "  eyepiece," 
because  it  is  nearest  to  the  observer's  eye.  The  objective 
collects  the  rays  of  light  from  the  object  under  examina- 
tion, bends  them  inward,  and  sends  them  to  the  focus. 
Here  they  form  a  minute  image  of  the  object.  At  the 
focus  they  cross  each  other  and  diverge  into  a  broadening 
stream.  Soon  they  reach  the  eyepiece,  which  further 


Lenses 

FIG.  5. — Microscope  objective. 

magnifies  the  image  and  again  bends  the  rays  and  directs 
them  to  the  eye  of  the  observer. 

The  objective  (Fig.  5)  is  detachable  and  can  be  un- 
screwed easily  from  the  microscope,  so  that  another 
objective  of  lower  or  higher  power  may  be  put  on  in  its 
place.  The  objective  is  the  most  powerful  and  the  most 
expensive  part  of  a  microscope.  In  a  very  good  instru- 
ment this  one  part  alone  may  cost  up  to  £25.  An 
advanced  worker  with  the  microscope  will  probably 
require  six,  or  more,  objectives. 


PLATE  IV 


\ 


r 
st 

0 

I 


THE  BINOCULAR  MICROSCOPE. 


21 


In  most  microscopes  to-day  there  is  only  one  tube, 
and  therefore  only  one  eye  can  be  used  for  observing. 
To  some  people  this  is  often  very  fatiguing  and  causes 
a  great  strain  upon  the  observer.  In  1860  Wenham 
invented  the  binocular  microscope, 
consisting  of  two  tubes  and  two  eye- 
pieces (Fig.  6).  By  an  ingenious 
device  two  images  are  formed  from 
one  object,  and  it  is  thus  made 
possible  to  employ  both  eyes  for 
observing.  The  binocular  micro- 
scope is  not  generally  used,  however, 
most  people  finding  the  single  tube 
instrument  satisfactory. 

III. 

From  the  description  I  have  just 
given  of  the  principles  of  the  micro- 
scope you  will  readily  understand 
that  the  glass  from  which  the  lenses 
are  made  plays  an  all-important 
part  in  its  construction.  It  was  be- 
cause of  a  defect  in  the  lenses  that 
the  microscopes  of  earlier  days  could 
not  be  developed  beyond  a  certain  point.  To  understand 
the  reason  of  this,  and  the  clever  manner  in  which  the 
difficulty  was  overcome,  it  is  necessary  to  learn  some- 
thing of  the  two  forms  of  lenses  used.  These  are  called 
"  convex  "  and  "  concave  "  (Fig.  7).  A  convex  lens  is 
thicker  in  the  middle  than  at  the  edges,  and  may  be  said 
to  bulge  outwards.  A  concave  lens  is  just  the  opposite, 


FIG.  6.  —  Section  of 
Binocular  Micro- 
scope. 


22  THE  MICROSCOPE. 

for  it  is  thicker  at  the  edges,  has  a  saucer-like  hollow  in 
the  centre,  sinking  inwards.  A  convex  lens  bends  or 
refracts  rays  inwards,  but  a  concave  lens  refracts  them 
outwards. 

Because  of  the  peculiar  shape  of  a  lens,  and  the  conse- 


CONVKX  CONCAVE 

ACHROMATIC 

FIG.  7. — Three  types  of  lenses. 

quent  difference  in  density  of  various  parts  where  it  is 
thicker  or  thinner,  the  rays  are  not  all  refracted  to  a 
similar  amount.  For  instance,  those  rays  which  fall 
near  the  edge  of  a  convex  lens  have  not  to  pass  through 
so  much  glass  as  those  rays  which  fall  on  or  near  the  centre 
of  the  lens.  Consequently,  on  passing  through  a  lens  the 
rays  follow  different  paths  and  do  not  all  meet  together 
exactly  at  the  focus.  A  distorted  and  blurred  image  is 
then  formed.  This  fault  is  called  "  spherical  aberration." 
It  can  be  overcome  by  fitting  into  the  uncorrected  lens 
a  second  lens,  of  a  different  shape  from  the  original. 
When  this  is  done  all  the  rays  are  brought  exactly  to  the 
same  focus. 

A  second  and  more  troublesome  defect  is  a  peculiar 
colouring — called  "  chromatic  aberration  " — caused  by 
the  lenses.  We  have  been  speaking  of  rays  of  light  for 
the  sake  of  clearness  and  as  though  they  formed  a  simple 
stream  of  light.  White  light  passing  through  a  prism 


THE  SPECTRUM.  23 

of  glass  issues  from  it  as  a  coloured  band.  No  doubt  you 
have  often  noticed  this  when  sunlight  falls  on  a  cut  glass 
pendant  of  a  chandelier  or  similar  object.  This  band  of 
coloured  light  is  called  the  spectrum  (Fig.  8).  It  con- 
tains certain  colours  which  merge  gradually  into  one 
another.  They  are  always  found  in  the  spectrum  in 
the  following  order :  red,  orange,  yellow,  green,  blue, 
indigo,  and  violet.  These  colours  are  combined  in  white 


FIG.  8. — How  the  spectrum  is  formed. 

light  and  are  therefore  invisible  to  us  in  ordinary  circum- 
stances. 

When  a  ray  of  light  passes  through  a  concave  or  convex 
lens  the  same  occurrence  takes  place  as  in  the  case  of  the 
prism.  The  white  light  is  broken  up  into  the  above- 
mentioned  colours.  Each  of  these  colours  has  what  is 
called  a  different  wave-length,  that  of  red  being  much 
longer  than  that  of  violet.  The  consequence  of  this,  in 
regard  to  the  microscope,  was  that  on  passing  through 
the  lenses  light  was  broken  up  into  its  component  colours 
of  varying  wave-lengths,  and  each  colour  gave  a  faint 
but  separate  image  of  the  object  under  examination. 
This  was  a  great  drawback,  of  course,  because  instead 
of  the  observer  seeing  a  clear,  well-focused  image  he  saw 


24  THE  MICROSCOPE. 

a  blurred  image  looking  like  "  all  the  colours  of  the 
rainbow." 

For  many  years  opticians  regarded  it  as  impossible 
to  overcome  chromatic  aberration.  Clearly  the  remedy 
was  to  bring  all  the  coloured  images  together  at  one  focus 
— in  other  words,  to  make  the  rays  all  of  the  same  wave- 
length. It  was  realized  that  unless  this  seemingly  im- 
possible task  could  be  effected,  the  compound  microscope 
could  never  be  perfect.  If  several  kinds  of  glass  of  differ- 
ent densities  could  have  been  used,  the  difficulty  might 
have  been  overcome.  This  seemed  a  forlorn  hope,  how- 
ever, for  only  two  kinds  of  glass  were  known,  crown 
and  flint  glass.  The  latter  kind  is  denser  than  the  former, 
and  with  a  lens  made  partly  of  each  it  was  possible  to 
correct  two  colours  ;  but  as  the  light-waves  of  the  other 
colours  remained  unconnected,  there  was  still  formed  a 
series  of  confusing  faint  images. 

IV. 

About  1881  two  Germans — Abbe,  Professor  of  Mathe- 
matics at  Jena,  and  Dr.  Schott,  who  was  interested  in 
glass-making — began  a  series  of  researches  and  experi- 
ments, aided  by  their  Government.  Professor  Abbe  had 
studied  optics  since  1873  and  worked  on  lines  which  were 
quite  original.  He  was  able  to  decide  on  paper  the 
density  he  required  the  glass  for  his  lenses,  and  also  exactly 
the  curve  the  surfaces  needed.  In  1884  a  microscope 
was  made  which  was  not  only  constructed  on  new  prin- 
ciples, but  had  lenses  of  a  new  kind  of  glass,  called  fluor- 
glass. 

To  understand  more  fully  the  value  of  this  advance 


PLATE  V 


THE  INVISIBLE  RAYS.  25 

in  the  construction  of  the  microscope  we  must  learn 
something  more  of  the  varying  lengths  of  the  light  rays. 
We  have  already  mentioned  that  violet  rays  are  shorter 
than  red  rays.  It  is  found  that  by  employing  the  shorter 
rays  more  details  in  a  minute  object  become  visible. 
In  fact,  so  much  is  this  the  case  that  by  violet  rays  objects 
may  be  distinguished  which  are  twice  as  small  as  those 
which  can  be  seen  by  the  longer  red  rays. 

The  violet  rays  are  not  the  shortest  of  all  known  waves 
of  light,  for  beyond  them  in  the  spectrum  are  the  ultra- 
violet rays  (see  Fig.  8) .  These  ultra-violet  rays  are  most 
curious,  for,  no  matter  how  long  we  may  look  at  the 
coloured  band  of  light  from  a  prism,  we  cannot  discern 
them.  They  are  invisible  to  the  human  eye  and  have 
never  been  seen,  for  their  length  is  so  short  that  they 
make  no  impression  upon  our  retina.  The  ultra-violet 
rays  can,  however,  be  photographed — or  rather  photo- 
graphs can  be  taken  by  them — and  so  we  know  of  their 
existence. 

We  can  now  better  understand  the  next  problem  which 
confronted  Professor  Abbe.  He  knew  that  by  means 
of  the  short  violet  rays  objects  which  could  not  be  seen 
with  the  long  red  rays  might  be  made  visible.  He 
believed  from  this  that  if  he  could  use  the  ultra-violet 
rays  he  would  be  able  to  make  the  microscope  many 
times  more  powerful  than  it  was,  even  with  the  violet 
rays.  To  attain  his  object  he  had  to  deal  with  rays  he 
could  not  see,  and  there  was  no  known  kind  of  glass  which 
was  capable  of  refracting  the  ultra-violet  rays  in  the 
same  way  in  which  crown  and  flint  glass  refract  the 
ordinary  rays. 

(2,084)  * 


26  THE  MICROSCOPE. 

Professor  Abbe  was  not  dismayed  by  such  difficulties 
as  these.  After  many  experiments,  the  firm  of  opticians 
with  whom  he  was  associated  succeeded  in  making  lenses 
of  molten  quartz.  These  lenses  could  be  used  to  refract 
the  ultra-violet  rays  as  required,  but  of  course  the  image 
formed  still  remained  invisible  to  the  human  eye.  Even 
Professor  Abbe  could  not  render  the  ultra-violet  rays 
optically  visible,  and  so  it  is  that  objects  can  only  be 
examined  by  these  rays  by  photography. 

Through  the  invention  of  quartz-glass  lenses  it  is  some- 
times possible  to  examine  objects  which  are  only  anrsuTT 
inch  hi  size. 

V. 

A  microscope  consists  of  the  following  important  parts, 
all  of  which  are  clearly  indicated  in  Fig.  9. 

(i)  The  body,  generally  a  brass  tube  which  carries,  at 
the  bottom,  (2)  the  objective,  and,  at  the  top  nearest  the 
observer's  eye,  (3)  the  eyepiece.  These  parts  are  mounted 
on  (4)  the  limb,  as  is  also  (5)  the  stage,  which  may  be  fitted 
with  spring  clips  for  holding  the  slide  or  object  to  be 
examined.  In  more  expensive  instruments  a  mechanical 
stage  is  fitted,  which  is  easily  moved  from  side  to  side  or 
upwards  and  downwards  by  milled-head  spindles  and 
rackwork.  Focusing  is  accomplished  by  (6)  coarse 
and  fine  adjustments,  and  a  light  is  reflected  on  to  the 
object  by  (7)  a  mirror,  fitted  by  a  sliding  clip  to  (8)  the 
tailpiece.  All  these  parts  are  mounted  on  (9)  the  foot  or 
base. 

If  the  object  we  are  examining  is  thin  and  sufficiently 
transparent  to  enable  light  to  pass  through  it,  it  is 


PARTS  OF  A  MICROSCOPE. 
Eyepiece 


27 


Draw tube 


Mi/led  head  for 
coarse  adjustment 


Moscpiece 
•  on  JBody 
for  Objective 

.  SfirintfC/ipa 

fornofdind 

Object 

Miffedhcad 
for  moving 
Mechanical 


Under-fitting 
Miffed  Avert 
for  raising 
Sub  stage 

S 


Mirror' 


FIG.  9. — Illustration  distinguishing  the  various  component  parts 
of  a  Compound  Microscope. 

placed  upon  the  stage  on  a  glass  slip  called  a  slide,  and 
light  is  reflected  to  it  by  the  mirror  (Fig.  10).  If  the 
object  is  opaque,  however,  and  it  is  impossible  for  light 


FIG.  10. — Illuminating  a  specimen  by  means  of  transmitted  light. 


FIG.  n. — Illuminating  a  specimen  by  reflected  light. 


PLATE  VI 


THE  CONDENSER.  29 

to  pass  through  it,  a  condenser  must  be  used  instead  of 
the  mirror.  The  condenser  consists  of  a  lens — generally 
mounted  on  a  separate  stand — which  throws  a  beam  of 
concentrated  light  on  to  the  object  from  above  the 
stage  (Fig.  n). 


CHAPTER  III. 
WORKING  WITH  THE  MICROSCOPE. 

I. 

OME  people  think  that  it  is  of  no  use  studying  any 
subject  unless  they  can  use  the  latest  and  most 
costly  instruments.  It  is  true  that  a  really  good  micro- 
scope is  expensive,  costing  anything  from  £5  to  £50  or 
even  more.  It  is  not  necessary,  however,  to  expend 
even  £5  on  a  microscope,  for  one  could  obtain  much 
entertainment  and  do  really  useful  work  with  a  "  home- 
made "  microscope,  which  does  not  cost  much  more 
than  55.  Microscopes  very  suitable  for  studying  the 
objects  described  in  these  pages  are  to  be  purchased  from 
£i  to  £5  second-hand.  There  are,  of  course,  many  objects 
— such  as  blood  corpuscles  and  bacteria — for  the  study 
of  which  more  powerful  objectives  are  required ;  but  we 
shall  find  that  a  simple  form  of  microscope  will  reveal 
sufficient  wonders  to  our  gaze  to  employ  us  for  many 
long  evenings. 

Galileo's  telescope  would  be  classed  as  a  very  crude 
instrument  in  these  days — indeed,  for  a  few  shillings  any 
one  can  make  an  equally  powerful  instrument.  But  in 
the  hands  of  Galileo,  this  little  "  optick  tube  "  explored 


USING  A  POCKET  LENS.  31 

the  heavens,  discovered  the  mountains  on  the  Moon,  the 
spots  on  the  Sun,  and  changed  man's  ideas  of  the  con- 
struction of  the  universe. 

In  his  Life  and  Letters  the  famous  scientist,  Charles 
Darwin,  says  the  student  should  always  see  what  he 
can  with  a  simple  microscope  before  using  a  compound 
instrument.  He  further  says  that  he  would  be  inclined 
to  suspect  the  work  of  a  man  who  never  used  the  simple 
instruments.  When  he  set  out  on  his  celebrated  voyage 
in  the  Beagle,  Darwin  took  with  him  only  a  simple  micro- 
scope, for  it  was  his  custom  to  use  simple  methods  and 
few  instruments  in  his  work. 

II. 

It  is  a  good  plan  to  spend  the  fine  days  of  summer  in 
collecting  objects.  After  examining  these,  put  away 
those  which  will  keep,  until  the  dark  nights  of  winter, 
when  sufficient  time  may  be  given  to  a  lengthy  and 
detailed  study  of  each.  For  examination  purposes  the 
pocket  lens  will  be  found  a  valuable  acquisition,  espe- 
cially if  it  is  used  correctly.  It  may  seem  unnecessary 
for  me  to  tell  you  how  to  use  a  pocket  lens,  but  for  those 
unaccustomed  to  handling  them  it  may  be  said  that  the 
best  way  to  look  at  an  object  is  first  to  put  the  lens 
close  to  the  eye  and  then  to  bring  it  down,  with  your 
head  following  it  at  the  same  time,  to  meet  the  object 
under  examination.  When  using  a  pocket  lens  it  is 
sometimes  desirable  to  have  one  hand  free  for  dissecting, 
and  the  difficulty  of  working  in  these  circumstances  has 
been  overcome  by  a  simple  device,  called  the  "  focostat  " 
(Fig.  12).  A  single  lens  is  mounted  by  a  movable  clip 


32  THE  MICROSCOPE. 

to  the  handle  of  the  dissecting  needle,  and  when  once 
the  lens  has  been  moved  to  the  correct  focus,  it  is  quite 


FIG.  12. — The  Focostat.    This  is  fixed  to  the  dissecting  needle, 
and  leaves  one  hand  free. 

easy  for  us  to  see  what  we  are  doing  with  the  needle 
point.    Another  way  of  working  so  that  one  hand  is  free 


FIG.  13. — The  "  Third  Hand  "  Magnifier. 

is  the  "  third-hand  "  magnifier,  as  it  is  called  (Fig.  13). 
This  consists  of  a  lens  which  is  attached  to  the  thumb 


PLATE  VII 


From  a  photo-micrograph  byj 


[A.  H.  Smith 


A    GROUP   OF    DIATOMS 


RECORDING  OBSERVATIONS.  33 

of  the  left  hand  by  a  clip,  similar  to  the  kind  which  are 
used  for  attaching  shades  to  candles. 

A  notebook  should  be  kept,  and  may  include  some 
record  of  where  and  how  the  specimens  were  obtained, 
and — later  on,  when  they  have  been  thoroughly  examined 
with  the  microscope — an  account  of  what  is  noticed 
about  them.  It  is  a  good  plan,  too,  to  make  as  many 
sketches  of  the  specimens  as  possible.  It  does  not 
matter  if  you  cannot  draw  or  paint,  for  even  the  roughest 
sketch  is  better  than  none  at  all.  It  is  found  that  by 
sketching  an  object  we  notice  details  which  might  other- 
wise escape  our  observation.  For  instance,  could  you 
describe  to  me  exactly  the  kind  of  chimney-pot  on  your 
house  ?  Perhaps  some  of  you  could,  but  many  could  not. 
Had  you  made  a  sketch  of  your  house  at  some  previous 
time  you  would  be  able  to  say  at  once  just  what  kind 
of  a  chimney  the  house  had,  because  in  making  your 
sketch  you  would  have  had  to  study  the  detail  of  the 
chimney-pots  in  order  to  draw  them  accurately. 

When  using  a  lens  or  a  microscope,  it  is  best  not  to 
shut  the  eye  which  is  not  being  used,  as  if  this  is  done  it 
will  soon  become  tired  with  being  screwed  up  for  any 
length  of  time.  With  a  little  practice  it  is  easy  to  train 
the  mind  to  see  only  with  the  eye  at  the  lens,  even  though 
the  other  eye  is  open. 

III. 

When  collecting  specimens  it  is  useful  to  take  two  or 
three  glass  tubes — the  kind  in  which  cachous  are  sold — 
and  if  possible  a  glass-topped  box.  If  we  are  collecting 
specimens  from  a  pond  we  take  a  small  glass  jar  or  a 

(2,084)  5 


34 


THE  MICROSCOPE. 


muslin  net  mounted  on  a  stick  (Fig.  14),  and  a  little 
drag,  made  by  inserting  three  or  four  wire  hooks  in  a 


FIG.  14. — (a)  Glass  jar  wired  to  stick. 
(b)  Muslin  net  mounted  on  stick. 


FIG.  15. — Drag  for  obtaining 
pond  weeds. 


piece  of  lead  fastened  to  the  end  of  a  string  (Fig.  15). 

With  this  we  can  pull  to  the  side  of  the  pond  pieces  of 

floating  twig  or  weed. 

A  large  bottle  should  also  be  taken,  and  if  possible  a 

second  one,  known  as  a  "  concentrating  bottle."  This  is 
best  made  by  obtaining  one  of  those  bottles 
with  a  metal  screw-top,  such  as  contain 
honey.  Punch  a  number  of  small  holes  in 
the  metal  top  and  solder  a  tin  funnel  in 
the  centre,  the  end  of  the  funnel-pipe  being 
a  few  inches  from  the  bottom  of  the  bottle 
(Fig.  16).  Before  screwing  on  the  lid, 

FIG.  16.— Con-  stretch  a  piece  of  fine  muslin  over  the  top 

bottLrating  of  the  bottle<     Water  poured  through  the 
funnel    in    the    bottle   will    now   overflow 
through  the  holes  in  the  lid,  but  the  specimens  it  con- 
tains are  prevented  from  leaving  the  bottle  by  the  muslin. 


COLLECTING  SPECIMENS.  35 

Thus  the  more  water  we  pour  into  the  bottle  the  more 
numerous  become  the  specimens  it  contains,  so  that  we 
take  home  with  us  in  our  bottle  specimens  contained  in 
bucketfuls  of  water. 

Another  useful  instrument  is  a  piece  of  glass  tubing, 
about  |  inch  or  one  inch  in  diameter.  One  end  is 
left  open,  but  at  the  other  a  piece  of  fine  muslin  is 
fastened  with  an  elastic  band.  The  tube  may  be  im- 
mersed in  the  pond  and  the  water  allowed  to  flow  through 
it.  The  water  passes  down  the  tube  and  out  at  the  end 
where  the  muslin  is  fastened.  The  muslin  acts  as  a 
strainer,  and  retains  minute  specimens  which  may  be 
easily  transferred  to  a  bottle  by  removing  the  elastic 
band. 

Single  specimens  may  be  obtained  by  using  a  piece  of 
glass  tube  open  at  both  ends.  Place  one  finger  over  one 
end  of  the  tube  and  lower  the  other  into  the  water  so 
that  the  end  comes  over  the  specimen  to  be  captured. 
If  we  take  away  our  finger  at  the  top  of  the  tube,  the 
water  rushes  up,  carrying  the  specimen  with  it.  By 
placing  the  finger  at  the  top  of  the  tube  again,  the  tube 
may  be  lifted  and  its  contents  released  into  a  jar. 

IV. 

Objects  for  observation  under  the  microscope  may  be 
divided  into  two  classes.  The  first  are  those  which  do 
not  require  any  preparation  and  may  be  observed  at 
once,  such  as  simple  plants.  The  greater  number  of 
objects  fall  into  the  second  class,  however,  and  are 
those  which  must  be  prepared  and  treated  before  all 
the  details  of  their  structure  may  be  made  out.  We  can 


36  THE  MICROSCOPE. 

illustrate  what  is  meant  by  this  by  taking  the  leg  of 
some  insect  and,  without  previous  preparation,  observing 
it  under  the  microscope.  We  see  nothing  but  a  dark 
opaque  body,  looking  like  a  silhouette,  with  possibly  a 
few  hairs  or  specks  of  dust  attached.  If  the  leg  be 
correctly  prepared,  however,  a  very  different  aspect  is 
presented.  In  the  first  place,  it  is  cleaned  and  rendered 
transparent ;  it  is  then  seen  to  be  beautifully  coloured, 
and  every  detail  becomes  visible.  The  delicate  muscles 
and  membranes  of  the  joints,  the  sharp  claws  and  soft 
pads  are  now  clearly  seen. 

For  the  observation  of  the  first  class  of  objects  a  live 
box  is  the  best.    This  consists  of  a  brass  cell  something 


FIG.  17. — A  live  box. 

like  a  pill-box  with  brass  sides  (Fig.  17).  The  bottom 
of  the  cell  is  formed  by  a  piece  of  glass ;  over  it  is  a  lid 
or  cover  with  a  glass  top  which  can  be  raised  or  lowered, 
so  as  to  press  on  the  bottom  glass  if  required.  This 
adjustment  is  very  useful  if  we  have  a  lively  insect  under 
observation,  for  we  can  gently  press  down  the  cover 
until  the  insect  is  trapped  and  held  secure  between  the 
two  glasses. 

In  observing  an  unprepared  section  of  some  fruit  or 
plant  it  is  best  to  place  it  on  a  glass  slide  and  cover  it 
with  a  drop  of  water,  placing  over  it  one  of  the  thin 
cover-glasses  used  for  the  purpose.  By  doing  so  not  only 
are  particles  of  dust  and  dirt  kept  from  the  object,  but 


PLATE  VIII 


DISSECTING.  37 

also  the  microscope  may  be  tilted  to  any  angle  re- 
quired, without  fear  that  the  object  will  fall  off  the  stage. 

V. 

Although  requiring  patience  and  perseverance,  the 
dissecting  or  cutting  up  of  insects  and  small  animals 
reveals  many  interesting  objects  and  teaches  us  much 
about  their  internal  structure.  One  of  the  first  things 
to  remember  is,  never  to  kill  any  creature  unless  you 
really  intend  to  learn  something  from  examination  of 
its  body.  Secondly,  always  make  quite  sure  that  your 
victim  is  dead  before  you  start  operating. 

Dissecting  under  the  compound  microscope  is  at  first 
somewhat  difficult.  Not  only  do  we  feel  awkward  in 
dealing  with  minute  objects  such  as  the  hairs  or  scales 
of  insects,  but  also  the  objects  become  inverted,  and 
changed  from  left  to  right  when  seen  in  the  microscope. 
After  a  little  practice,  however,  this  state  of  affairs 
becomes  quite  natural.  Dissections  should  be  carried 
out  under  water,  contained  in  a  shallow  trough.  A 
porcelain  dish,  such  as  is  used  for  mixing  water-colour 
paints,  or  a  watch-glass  will  do  admirably  for  the  pur- 
pose. More  delicate  work  may  be  accomplished  in  a 
drop  of  water  placed  on  a  glass  slide. 

If  we  are  anxious  to  learn  what  is  inside  an  insect, 
such  as  a  bee  or  a  fly,  and  the  object  is  too  large  to  be 
dissected  under  even  the  lowest  power  of  our  microscope, 
we  may  carry  out  the  first  part  of  the  operation  under  a 
simple  magnifying  glass.  This  should  be  firmly  mounted 
in  a  temporary  stand,  thus  leaving  both  hands  free  for 
operating.  Having  cut  the  insect  open,  extracted  its 


38  THE  MICROSCOPE. 

internal  organs  and  separated  the  limbs  from  its  body, 
we  may  proceed  to  examine  them  with  the  higher  powered 
microscope. 

When  insects  have  been  killed  for  any  length  of  time 
their  bodies  become  hard  and  brittle.  They  may  be 
softened  by  steeping  them  in  a  dilute  solution  of  caustic 
potash  (liquor  potass a),  which  may  be  obtained  from  a 
chemist. 

Instruments  for  dissecting  may  be  purchased  from 
almost  any  firm  of  opticians,  but  the 
simple  ones  required  by  the  beginner 
may  be  easily  made  at  home,  with 
the  exception  of  a  pair  of  tweezers 
which  must  be  purchased  (Fig.  18). 
It  is  only  waste  of  money  for  us  to 
purchase  an  expensive  outfit  of  "  tools " 
before  we  see  if  we  like  dissecting  work  ; 
because,  as  I  have  already  mentioned,  it 
requires  a  good  deal  of  patience  and  per- 
severance. 

For  simple  dissections  we  shall  require 
three  dipping-tubes,  somewhat  similar  to 
those  used  in  collecting  objects  (Fig.  19). 
These  may  be  made  by  obtaining  some  glass 
tubing  from  a  chemist.  The  first  is  simply 
a  length  of  about  six  inches,  and  may  be 
cut  to  size  by  filing  a  groove  around  the 
tubing  with  a  nail  file.  On  giving  the  tubing 
a  sharp  blow  the  required  length  will  break 
off.  The  second  is  made  by  heating  the  centre  of  a  length 
of  tubing  until  it  becomes  soft.  Take  a  firm  hold  of 


\ 


FIG.  19. — 
Glass  tubes. 


DISSECTING  INSTRUMENTS.  39 

both  ends  and  draw  them  out,  allow  the  tube  to  cool, 
file  around  the  centre  as  in  the  previous  case,  and  break 
off.  The  third  tube  is  made  similarly  to  the  second, 
except  that  while  hot,  and  after  being  drawn  out,  the 
tube  is  bent  to  the  required  curvature. 

Three  needles  should  now  be  mounted  in  wooden 
handles  —  ordinary  sewing  needles  pushed 
into  wooden  penholders  will  do  very  well 
(Fig.  20).  The  first  should  be  left  straight, 
the  second  bent  in  a  flame  to  a  right  angle, 
the  third  curved  to  a  similar  shape  to  the 
third  dipping -tube.  The  joint  where  the 
needles  enter  the  handle  may  be  bound 
round  with  thread,  and  the  whole  varnished 
over  with  shellac. 

With  this   modest    equipment,  a  pair  of 
sharp    nail    scissors,   and   a  good    penknife       . 
sharpened  and  ground  to  a  razor-like  edge,      Dissecting 
we   can   find   sufficient   work    before   us   to 
employ  all  the  spare  hours  of  many  a  winter's  night. 


CHAPTER  IV. 
MICROSCOPIC  PLANTS. 

I. 

IN  almost  any  pond  will  be  seen  an  abundant  supply 
of  minute  life,  both  plants  and  animals.  In  some 
ponds,  especially  those  in  which  the  water  is  green  and 
stagnant,  life  abounds  in  every  drop  of  water.  Each 
object  examined  under  the  microscope  will  afford  us  a 
fund  of  knowledge.  Even  from  the  lowliest  forms  of 
pond  life  we  can  learn  a  great  deal  which  will  help  us 
when  we  come  to  study  the  higher  and  more  complicated 
forms  of  vegetable  and  animal  life. 

Microscopic  objects  may  be  found  either  floating  on 
the  surface  or  swimming  in  the  water,  while  a  large 
number  are  to  be  found  only  at  the  bottom  of  the  pond, 
embedded  in  the  sand  or  mud.  We  have  already  seen 
how  to  collect  such  objects,  and  we  will  assume  that  we 
have  paid  a  visit  to  a  suitable  pond  and  returned  with 
a  good  "  bag  " — or  rather,  in  this  case,  a  full  bottle. 
After  allowing  the  water  to  stand  a  short  time  and  the 
contents  to  settle,  we  may  commence  to  examine  it, 
taking  up  a  little  at  a  time  in  the  pipette  or  dipping-tube — 
already  described — and  placing  it  in  the  live  box.  An 

40 


PLATE    IX 


^--colour  clrawing  by] 

A  swarm  of  Euglena  viridis  near  the  surface 
of  a  stagnant  pond 


10.  Fisher-Jones 


DESMIDS.  41 

easy  way  to  quickly  examine  a  quantity  of  water  is  to 
employ  one  of  the  small  syringes  used  in  filling  fountain 
pens. 

One  of  the  first  things  we  are  sure  to  see  are  bright 
green  objects  of  various  shapes.  These  are  called  desmids, 
and  they  are  well-known  microscopic  plants.  When 
plants  are  mentioned  some  people  at  once  think  of  the 
flowering  plants  in  our  gardens,  or  the  plants  which  we 
have  in  pots  and  vases  in  our  homes.  These  kinds  of 
plants  form  only  a  small  proportion  of  the  plant  life 
of  the  world,  however,  for  there  are  many  other  speci- 
mens of  plants  of  the  existence  of  which  most  people  are 
quite  ignorant.  Some  of  these  plants  are  to  be  found 
in  the  most  unlikely  places.  Would  you  ever  think, 
for  instance,  of  expecting  to  find  interesting  forms  of 
plant  life  in  a  rotting  wooden  fence  or  an  old  tree  trunk  ? 
Yet  it  is  probably  no  exaggeration  to  say  that  in  such 
a  place  it  is  possible  to  find  more  varieties  of  microscopic 
plant  life  than  there  are  examples  of  the  higher  orders 
in  the  Botanical  Gardens  at  Kew. 

II. 

The  Desmids  are  an  extensive  family  of  plants 
composed  only  of  a  single  cell.  They  are  placed  at 
the  bottom  rung  of  the  ladder  of  botanical  classifica- 
tion. Desmids  live  in  fresh  water ;  in  some  ponds  they 
are  so  numerous  as  to  cause  the  water  to  assume  a  decided 
greenish  colour. 

In  addition  to  presenting  a  very  beautiful  appearance 
the  presence  of  this  bright  green  colour  is  useful  to  the 
microscopist,  for  it  enables  the  desmids  to  be  rapidly 

(2,084)  6 


42  THE  MICROSCOPE. 

distinguished  from  most  other  one-celled  plants.  The 
green  colouring  matter  in  desmids,  and  in  all  other  plants 
also,  is  called  chlorophyll.  This  name  comes  from  the 
Greek  word  chloros,  meaning  "green,"  and  by  the  pres- 
ence of  chlorophyll  members  of  the  vegetable  kingdom 
are  easily  distinguished.  How  important  this  aid  is  we 
shall  see  later,  for  it  is  sometimes  almost  impossible  to 
say  whether  a  minute  object  is  a  vegetable  or  an  animal 
from  its  shape  alone. 

Desmids  are  found  in  all  manner  of  shapes,  and  there 
are  so  many  varieties  of  them  that  they  have  been 
divided  into  groups  to  help  in  their  identification.  They 
present  so  many  interesting  problems,  indeed,  that  books 
have  been  written  on  them  alone. 

Some  desmids  are  more  or  less  irregular  in  form,  like 
Euastrum,  which  consists  of  two  main  portions  of  a 
bright  green  colour,  joined  together  by  a  narrow  waist- 
like  piece.  Its  edges  are  notched  and  indented,  and 
it  is  covered  with  dark  green  spots  (d,  Plate  II.).  An- 
other variety  is  the  crescent-shaped  Closterium,  of  which 
there  are  several  species,  although  all  are  of  the  same 
general  shape  (b,  Plate  II.).  Sometimes  the  green  cells 
are  surrounded  by  a  transparent  substance  like  gelatine  ; 
occasionally  this  is  so  indistinct  as  to  be  almost  invisible. 

Often  several  of  these  minute  plants  are  found  joined 
together,  forming  what  looks  something  like  part  of  a 
bamboo  cane  with  notched  edges  (c,  Plate  II.).  This 
type  is  called  Desmidium,  and  from  it  the  desmids  take 
their  name.  The  variety  called  Scenedesmus  also  consists 
of  several  cells  joined  together,  the  last  two  cells  having 
hair-like  projections  (/,  Plate  II.).  Another  desmid  of 


DESMIDS.  43 

a  somewhat  similar  kind  is  Pediastrum  ;  here  the  cells 
unite  and  form  a  rounded  mass.  Each  cell  has  pro- 
jections, and  the  whole  colony  presents  a  beautiful 
appearance  (e,  Plate  II.). 

A  peculiar  feature  of  the  desmids  is  their  constant 
movement  through  the  water  in  which  they  live.  How 
this  movement  is  accomplished  is  as  yet  undecided. 
It  may  be  that  each  cell  has  a  large  number  of  very 
fine  hair-like  organs  which,  like  the  oars  of  a  boat,  row 
the  plant  along,  as  is  known  in  the  case  of  some  other 
minute  plants  which  we  shall  consider  later.  Or  perhaps 
the  explanation  is  to  be  found  in  the  fact  that  the  cells 
give  off  some  sort  of  exudation  or  discharge,  and  that 
this  act  causes  them  to  move  through  the  water. 

When  a  desmid  is  fully  grown  it  breaks  up  into  two 
portions,  and  these  commence  to  grow  ;  later  they  them- 
selves divide.  It  is  in  this  way  that  these  minute  plants 
multiply.  They  illustrate  for  us  the  simplest  mode  of 
reproduction  in  Nature,  that  of  cell-division.  Often  we 
may  watch  this  division  taking  place,  or  see  different 
desmids  in  various  stages  of  breaking  up. 

Take,  for  instance,  Closterium,  several  specimens  of 
which  we  are  almost  sure  to  find  in  a  bottleful  of  water 
from  some  pond.  Here  is  a  young  plant  exhibiting 
a  peculiar  marking  like  a  faint  belt  across  its  centre 
(a,  Fig.  21).  As  the  tiny  desmid  grows  this  marking 
becomes  more  and  more  pronounced  and  soon  becomes 
a  notch,  or  "  waist,"  so  that  it  would  seem  almost  as 
though  some  one  had  tied  an  invisible  rope  around  the 
centre  and  that  this  rope  is  being  drawn  tighter  and 
tighter  as  time  goes  on  (b,  Fig.  21).  The  waist  becomes 


44 


THE  MICROSCOPE. 


narrower  and  narrower  until  at  last  the  plant  divides 
completely  in  half  and  we  find  we  have  two  new  speci- 


FIG.  21. — Closterium,  a  microscopic  plant,     (a)  Natural  view. 
(6)  Dividing,     (c)  Two  plants. 

mens  of  Closterium  (c,  Fig.  21).  If  we  examine  the  two 
halves  carefully  we  can  already  see  signs  of  the  formation 
of  another  waist-belt,  ready  for  the  time  when  the  two 
halves  will  themselves  again  divide. 

III. 

Another  family  of  one-celled  plants  is  the  Diatoms. 
They  are  even  more  numerous  and  more  common  than 
the  desmids,  which  they  resemble  in  many  ways.  There 
is,  however,  one  great  difference.  When  a  desmid  dies 
its  substance  becomes  decomposed  and  perishes.  On 
the  other  hand,  a  diatom  is  almost  indestructible,  for  it 
is  surrounded  by  a  hard,  flinty  shell.  This  shell,  or 
outer  skeleton  as  it  is  sometimes  called,  is  constructed 
of  silica,  extracted  by  the  diatom  from  the  water  in 
which  it  lives.  Thus,  though  we  are  able  only  to  examine 


PLATE    X 


From  a  water-colour  drawing  byl  [G.  Fisher-J< 

i.   Mcliccrta  ringens.         2.   Rotifer  vulgaris.         3.  Parajticpciuin  a?irelia. 

4.   A  very  young  Mclicerta  which  lias  been  placed  a  second 

time  in  water  coloured  by  carmine. 


DIATOMS.  45 

living — or  very  recently  dead — desmids,  it  is  possible  to 
examine  the  shell-cases  of  diatoms,  the  owners  of  which 
have  been  dead  some  time.  In  fact,  so  successfully  do 
they  resist  the  ravages  of  time  and  of  the  elements  that 
the  skeletons  of  diatoms  which  lived  thousands  of  years 
ago  are  still  perfectly  preserved  in  some  of  the  rocks  of 
the  Earth. 

The  first  known  forms  of  diatoms  were  discovered 
towards  the  close  of  the  eighteenth  century  by  Miiller. 
In  1824  Agardh  published  his  book,  Sy sterna  algarum, 
describing  nine  varieties  of  diatoms.  Now  over  10,000 
species  are  known,  and  about  1,200  of  these  are  found  in 
the  fresh  waters  and  around  the  coasts  of  Great  Britain 
and  Ireland. 

Diatoms  are  found  everywhere  in  all  the  known  waters 
of  the  Earth.  We  may  safely  say  that,  wherever  there 
is  moisture  and  light,  there  too  will  diatoms  be  found — 
in  ditches,  ponds,  and  in  mountain  tarns ;  on  moist  rocks, 
and  as  a  deposit  of  brownish  mud  in  streams  and  pools. 
They  live  in  countless  millions  in  our  oceans,  and  in 
some  estuaries  they  are  so  abundant  that  they  play  an 
important  part  in  diminishing  the  depths  of  channels. 
In  some  cases  they  have  been  known  even  to  block  up 
harbours. 

In  the  microscope  a  diatom  looks  like  a  fragment  of  a 
beautifully  engraved  diamond,  and  no  one  can  see  these 
objects  without  an  expression  of  wonder  at  their  delicate 
beauty.  Diatoms  are  of  all  imaginable  shapes  and, 
unlike  the  bright  green  desmids,  are  of  a  golden-brown 
colour.  Some  are  disc-shaped,  like  Craspedodiscus, 
which  is  beautifully  marked  (a,  Plate  III.).  Others 


46  THE  MICROSCOPE. 

resemble  squares  joined  together,  like  Melosira.  Some, 
again,  are  triangular,  like  Triceratium  (b,  Plate  IV.). 
Perhaps  the  commonest  variety  is  the  oval  or  boat- 
shaped  diatom,  of  which  Pinnularia  and  Navicula  are 
examples  (Plate  V.). 

Diatoms  are  of  all  sizes,  a  "  giant  "  measuring  as  much 
as  -g^  inch  in  length  ;  but  the  majority  are  less  than  TTrV^ 
inch  in  size.  Their  shells  are  often  of  most  exquisite 
design,  and  are  covered  with  delicate  markings,  and  minute 
holes  or  pores.  The  fine  lines  of  the  diatoms  will  illustrate 
for  us  the  power  of  a  microscope.  If  we  were  to  draw  two 
lines  very  carefully  only  T-^  inch  apart,  the  space  between 
them  would  only  just  be  visible  as  a  white  line.  To 
represent  the  lines  on  some  diatoms  we  should  have  to 
divide  this  space  of  T^  inch  into  over  500  spaces. 
The  lines  on  some  diatoms  are  even  finer,  and  to  repre- 
sent them  correctly  the  T^  inch  space  would  require 
to  be  divided  into  over  900  spaces  !  These  lines  are  often 
used  as  objects  with  which  to  test  the  power  and  quality 
of  microscopic  objectives. 

The  markings  on  diatom  shells  have  been  the  sub- 
ject of  endless  discussion.  The  most  expert  workers  and 
the  finest  lenses  have  been  employed  in  the  endeavour 
to  find  out  what  exactly  is  the  meaning  of  the  numerous 
lines  and  pores  with  which  diatoms  are  covered.  So 
fascinating  is  their  study,  indeed,  that  some  scientists 
have  been  influenced  to  put  aside  all  other  microscopical 
work  in  order  that  the  whole  of  their  time  might  be  de- 
voted to  diatoms.  Because  of  this,  and  because  these 
scientists  so  often  talk  and  write  about  these  beauti- 
ful little  creatures,  they  have  sometimes  been  called 


DIATOMS.  47 

"  diatomaniacs  "  by  rude  and  ignorant  people  who  do 
not  understand  these  things. 

Diatoms  derive  their  name  from  two  Greek  words, 
dia,  "  across,"  and  tome,  "  cut,"  because  each  shell  is  cut 
or  divided  into  two  parts,  called  the  frustules.  One  of 
these  frustules  overlaps  the  other,  fitting  on  it  like  the  lid 
of  a  pill-box. 

Like  the  desmids,  diatoms  reproduce  themselves  by 
simple  cell-division,  a  single  diatom  dividing  into  two. 
So  quickly  can  they  multiply  in  this  way  that  it  has 
been  calculated  over  1,000,000,000  diatoms  may  be 
produced  from  a  single  parent  in  a  month,  under  favour- 
able conditions. 

When  a  diatom  dies  its  shell  sinks  through  the  water 
and  falls  to  the  bottom  of  the  pond  or  ocean.  So  numer- 
ous do  these  shell-cases  or  skeletons  become  that  they 
form  a  kind  of  mud  or  sediment,  called  diatomaceous 
ooze.  Deep-sea  soundings  have  shown  that  some  of 
these  deposits  are  of  very  great  extent.  Off  the  shores 
of  Victoria  Land,  for  instance,  in  70°  south  latitude,  at 
a  depth  of  between  200  and  400  feet,  is  a  deposit  of  mud. 
This  extends  not  less  than  400  miles  in  length  and  120 
miles  in  breadth,  and  is  chiefly  composed  of  the  shell- 
cases  of  diatoms.  In  the  course  of  ages — thousands 
upon  thousands  of  years,  perhaps — this  mud  may  be 
hardened  into  a  solid  rock,  which  may  be  lifted  above 
the  ocean  by  movement  of  the  Earth's  crust.  This  is 
actually  what  has  happened  in  the  case  of  some  rocks 
which  are  found  to-day  high  and  dry  above  the  ocean  in 
many  parts  of  the  world. 

In  Bohemia,  rocks  composed  of  the  fossil  shells  of 


48  THE  MICROSCOPE. 

diatoms  which  lived  years  ago  are  found  in  beds  which 
are  fourteen  feet  thick.  More  wonderful  still  are  the 
deposits  at  Richmond,  Virginia,  U.S.A.  They  are  re- 
markable both  on  account  of  their  extent  and  because 
of  the  number  and  beauty  of  the  specimens  of  diatoms 
they  contain.  Here  the  skeletons  of  long-dead  diatoms 
form  a  bed  extending  over  many  miles,  and  at  some 
places  the  rock  is  at  least  forty  feet  in  thickness.  It  is 
impossible  for  us  to  imagine  the  number  of  minute 
diatom  shells  required  to  form  a  deposit  so  great.  We 
may  obtain  some  idea  of  the  immense  numbers  from 
particulars  of  a  block  of  diatom  deposit  to  be  seen  in 
the  botanical  section  of  the  British  Museum.  This 
block  measures  only  two  cubic  feet  in  bulk,  and  was 
obtained  from  a  fresh-water  lake  in  Australia.  It  is 
estimated  that  it  contains  more  than  twelve  billions 
of  fossil  diatoms  ! 

IV. 

One  of  the  most  beautiful  objects  found  in  pond  water 
is  Volvox  globator.  Through  the  microscope  Volvox 
resembles  a  beautiful  lace-like  tracery,  more  delicate 
than  a  spider's  web  (see  Frontispiece).  This  covering 
is  studded  with  minute  green  spots,  each  of  which  ter- 
minates in  two  long  cilia,  or  gossamer-like  hairs.  It  is 
believed  that  it  is  by  the  aid  of  these  cilia  that  Volvox 
is  able  to  swim,  for  they  are  constantly  in  movement, 
thrashing  the  water.  Healthy  specimens  are  always 
in  motion,  gliding  gracefully  along,  and  resembling  at 
tunes  minute  revolving  worlds.  It  was  this  extraor- 
dinary power  of  moving  from  place  to  place  which  at 


PLATE    XI 


VOLVOX.  49 

one  time  led  microscopists  to  think  that  Volvox  was  an 
animal,  and  controversy  raged  over  the  question  for  a 
long  time.  Volvox  was  first  classified  in  the  animal 
kingdom,  but  at  last  it  was  definitely  described  as  being 
a  true  plant. 

The  green  spots,  already  referred  to,  give  Volvox  the 
appearance  of  a  minute  knitted  ball  of  orange-tinted 
green  silk,  and  very  exquisite  it  looks.  It  is  possible  to 
see  through  the  outer  lace-like  sphere,  and  often  smaller 
green  globes  are  visible  within  the  network.  These  tiny 
globes  are  really  young  Volvoces.  Sometimes  they  are 
six  or  eight  in  number,  but  in  some  cases  as  many  as 
twenty  have  been  counted.  Occasionally  even  a  third 
generation  may  be  seen  inside  the  young  Volvoces  them- 
selves. 

As  time  goes  on,  the  young  Volvoces  develop  until 
there  comes  a  day  when  they  are  sufficiently  grown  to 
shift  for  themselves.  They  break  through  the  sphere 
in  which  they  were  born,  the  sides  of  their  mother  open- 
ing to  allow  them  to  glide  through.  At  first  they  are 
attached  to  their  parent  by  long  filaments,  but  they  soon 
tire  of  being  tied  by  these  "  apron-strings."  They 
break  away,  commence  life  on  their  own  account,  and 
soon  grow  to  the  size  of  the  parent  Volvox. 

Volvox  is  not  a  single  cell,  like  the  desmids  and  diatoms, 
although  it  is  included  in  the  same  botanical  classifica- 
tion. It  really  belongs  to  a  higher  organization,  being 
a  colony  or  assemblage  of  minute  cells,  just  as  a  daisy 
is  a  composite  flower.  It  is  to  be  found  in  those  clear, 
fresh-water  pools  which  are  open  to  sunlight,  for  like 
most  plants  it  is  fond  of  sunshine.  The  water  of  some 

(2,084)  7 


50  THE  MICROSCOPE. 

ponds  is  so  full  of  Volvoces  that  when  held  up  to  the 
light  in  a  glass  jar  it  seems  to  be  of  a  semi-transparent 
green  colour. 

Volvo x  measures  from  about  ^  to  ^  mc^  i*1  size- 
The  larger  specimens  may  be  seen  easily  with  the  naked 
eye,  looking  like  minute  specks  of  green  matter.  Be- 
cause of  its  incessant  movement,  already  mentioned, 
Volvox  is  often  a  difficult  object  to  photograph  or  draw 
correctly  in  detail  (Plate  VIII.). 

V. 

In  pond  water  we  often  find,  in  addition  to  desmids  and 
diatoms,  several  other  forms  of  vegetable  life.  Some- 
times we  may  come  across  long,  green  filaments  of  a 
variety  of  forms.  These  are  the  fronds  of  conferva,  and 
they  are  composed  of  a  number  of  cells  growing  together 
and  looking  somewhat  like  a  bamboo  cane.  As  in  the 
case  of  the  desmids  and  other  plants,  they  too  owe  their 
green  colour  to  the  chlorophyll  they  contain.  In  some 
species,  as  in  Zygnema,  the  chlorophyll  is  found  formed 
in  spirals  (Fig.  22). 

Often  two  specimens  of  these  plants  may  be  seen  to 
join  or  fuse  together  and  the  contents  of  one  are  trans- 
ferred to  the  other,  bead-like  objects — called  spores — 
being  formed  (b,  Fig.  22).  Spores  are  the  first  stage  in  the 
life-history  of  the  lower  plants — such  as  seaweed,  fungi, 
mosses,  and  ferns.  Just  as  flowering  plants  grow  from 
seeds,  so  do  the  lower  plants  spring  from  spores. 
Perhaps  the  most  familiar  spores  are  the  masses  of 
brown  powder  on  the  under-side  of  the  frond  of  a  fern. 
Spores  are  very  minute,  and  when  ripe  are  scattered  by 


ZOOSPORES.  51 

the  wind  or  water.  The  spores  of  some  fungi  and  sea- 
weeds disperse  themselves  by  being  able  to  swim  in  the 
water,  and  afford  examples  of  free  movement  in  the 
plant  world.  Because  of  this  resemblance  to  animals — 


if 


a  is  c  a 

FIG.  22. — Zygnema,  a  microscopic  plant,  (a)  Showing  the  chlorophyll 
spirals.  (6)  Formation  of  spores,  (c)  Zoospores  leaving  the  plant. 
(d)  A  zoospore,  showing  cilia. 


their  being  able  to  move  about — these  spores  are  called 
zoospores. 

In  the  case  of  Zygnema,  which  we  have  already  men- 
tioned, zoospores  are  sometimes  formed  instead  of  the 
ordinary  spores.  When  this  occurs,  the  contents  of  the 
cells  draw  together  and  form  the  zoospores  (c,  Fig.  22), 
which  then  break  away  from  the  parent  cell  and  move 
rapidly  about  through  the  water  in  all  directions,  by 
means  of  cilia,  or  fine  hair-like  appendages. 

Occasionally  zoospores  gather  together  and  move 
rapidly  about  in  a  sphere.  A  common  example  of  this 


52  THE  MICROSCOPE. 

class  of  object  is  Pandorina  Morum  (Fig.  23),  each  spore 

in  the  colony  of  which  possesses  two  cilia. 

Sometimes  in  our  examination  of  pond 
water  we  come  across  a  queer-looking 
object,  called  Euglena  viridis  (Plate  IX.). 
In  some  ponds  they  exist  in  such  large 

FIG.  23.— Pan-    numbers  as  to  make  the  water  look  like 

donna  Morum.  _t  ,  J .  . 

pea-soup.  The  appearance  of  this  minute 
plant  in  the  microscope  is  remarkable,  for  it  resembles 
nothing  so  much  as  a  sole  or  similar  fish.  It  is  of  a 
green  colour,  with  a  red  spot,  which  we  may  imagine 
to  be  its  eye,  at  one  end  and  a  kind  of  drawn-out  tail 
at  the  other.  Its  appearance  is  deceptive,  and  it  may 
easily  be  mistaken  for  a  member  of  the  animal  kingdom, 
although  it  is  really  a  plant  with  extraordinary  powers 
of  locomotion,  like  Volvox  or  Pandorina  Morum. 


PLATE    XII 


From  a  w&'er-cr>lnnr  drawing  by] 


[G.  Fisher-Jones 


Stephanoceros   Eichorni! 


XJ 


CHAPTER   V. 
MICROSCOPIC  ANIMALS. 

I. 

IF  I  were  to  ask  if  you  could  always  distinguish 
between  an  animal  and  a  vegetable,  you  would 
possibly  think  that  I  did  not  give  you  credit  for  possess- 
ing much  intelligence.  It  is  true  that  when  we  have  in 
mind  some  of  the  more  highly  developed  members  of 
either  kingdom,  say  a  cat  and  a  cabbage,  the  difference 
is  very  pronounced.  But  among  the  more  lowly  members 
of  these  kingdoms,  members  which  interest  us  more  at 
present  because  they  are  to  be  seen  in  detail  only  with 
a  microscope,  the  difference  is  not  so  apparent.  For 
instance,  could  you  tell  me — without  referring  to  books — 
whether  a  sponge  is  of  an  animal  or  a  vegetable  nature  ? 
As  a  matter  of  fact,  it  represents  a  colony  of  animals 
which  are  more  highly  developed  than  many  animals 
having  bodies  with  heads,  mouths,  and  tails,  and  which 
are  not — as  the  sponge  generally  is — fastened  to  a 
re  *  but  swim  freely  about  in  the  waters  of  the  ocean. 
Appear;  ices  are  deceptive,  however,  for  many  vegetable 
organisms  seem  to  bear  a  closer  resemblance  to  animals 
than  does  a  sponge. 


34  THE  MICROSCOPE. 

The  problem  of  deciding  whether  certain  microscopic 
organisms  belong  to  the  animal  or  the  vegetable  king- 
dom has  occupied  the  attention  of  some  of  our  most 
distinguished  scientists,  and  given  rise  to  endless  discus- 
sions. At  one  time  it  was  thought  that  we  could  be 
guided  in  deciding  if  an  organism  was  an  animal  or  a 
vegetable  by  the  green  colouring  matter  called  chloro- 
phyll, the  presence  of  which  was  believed  to  indicate 
that  an  organism  was  certainly  a  true  plant.  Distinc- 
tion by  these  means  became  difficult,  however,  when 
later  on  it  was  found  that  chlorophyll  existed  in  some 
of  the  minute  forms  of  animal  life,  called  animalcules. 
On  the  other  hand,  it  was  found  that  the  substance 
called  cellulose,  of  which  the  walls  of  plant  cells  are 
composed,  enters  into  the  composition  of  certain 
animalcules  found  in  the  sea. 

Nor  are  we  helped  in  distinguishing  between  plants 
and  animals  according  to  whether  or  not  the  organism 
has  powers  of  locomotion.  We  generally  imagine  an 
animal  as  being  able  to  move  from  place  to  place,  and 
a  plant  as  being  permanently  stationary.  As  we  have 
already  seen,  however,  the  plant  Volvox  is  provided 
with  organs  which  enable  it  to  move  about.  On  the 
other  hand,  there  are  forms  of  animals  which  are  always 
fixed  to  one  place.  To  add  to  the  uncertainty,  some 
organisms  seem  almost  to  have  an  animal  form  of  exist- 
ence at  one  period  of  their  life-history,  and  a  vegetable 
form  at  another.  A  well-known  instance  of  this  is  the 
yellow  fungus  which  is  found  in  tan-pits,  called  jEthalium, 
or  "  flowers  of  tan."  Not  only  does  it  move  about  from 
place  to  place,  but  it  also  actually  feeds  upon  solids. 


SIMPLE  PLANTS  AND  ANIMALS.  55 

One  of  the  most  certain  methods  of  distinguishing 
between  one-celled  plants  and  one-celled  animals  is  the 
difference  in  the  method  of  obtaining  food  or  nutrition, 
as  it  is  called.  A  green  plant  is  able  to  live  independently 
of  other  organisms,  by  the  help  of  light,  heat,  and  mois- 
ture. It  builds  up  its  substance  from  simple  gases  con- 
tained in  the  air  and  from  solutions  of  inorganic  salts, 
found  in  the  soil  or  water.  On  the  other  hand,  an  animal 
can  live  practically  independently  of  sunlight,  but  it 
cannot  exist  apart  from  other  living  organisms,  for  it 
depends  upon  them  for  its  sustenance.  It  is  unable  to 
build  up  its  structure  from  simple  chemical  constituents, 
as  a  plant  does,  but  must  be  supplied  with  ready-made 
proteids.  By  remembering  these  facts  we  are  some- 
times able  to  say  to  which  kingdom  some  microscopic 
form  of  life  belongs,  when  otherwise  we  might  have  to 
admit  a  doubt. 

From  what  I  have  just  said  you  will  easily  understand 
that  it  has  become  very  clear  that  the  distinction  be- 
tween some  of  the  simplest  forms  of  plant  and  animal 
life  is  occasionally  so  obscure  and  indefinite  that  it  does 
seem  as  though  no  definite  dividing  line  can  be  drawn 
between  the  two  kingdoms.  It  seems  probable,  indeed, 
that  the  two  kingdoms  do  actually  merge  into  each  other 
by  imperceptible  degrees. 

II. 

Wherever  we  find  one-celled  plants  we  may  be  almost 
certain  to  find  also  animals  to  feed  upon  them.  Just  as 
there  are  one-celled  plants  at  the  bottom  of  the  ladder 
of  botanical  classification,  so,  too,  there  are  one-celled 


56  THE  MICROSCOPE. 

animals  which  occupy  a  similar  position  in  the  classifica- 
tion of  their  kingdom.  They  belong  to  a  class  called 
the  Protozoa,  from  the  Greek  word  proton,  "  first,"  and 
zoon,  "  living  thing."  They  are  among  the  lowest  forms 
of  animal  life.  Each  is  composed  of  a  single  cell  of 
living  matter,  a  minute  speck  of  jelly-like  substance, 
without  limbs  of  any  sort.  Each  cell  is  complete  in 


Fie.  24. — Amoeba,     (a)  and  (c)  Showing  nuclei,  vacuoles  and 
pseudopodia.     (&)  Formation  of  two  amoeba?. 

itself,  however,  and  can  move,  feed,  breathe,  and  re- 
produce others  of  its  kind. 

One  of  the  best  known  is  the  Amaba,  found  both  in 
fresh  and  in  salt  water,  but  more  often  in  the  sediment 
of  ponds  and  rivers  (Fig.  24).  Amoeba  looks  like  a 
speck  of  jelly,  for  it  is  almost  transparent.  Sometimes 
it  seems  to  be  merged  in  the  water  in  which  it  floats,  so 
that  it  is  difficult  to  say  where  the  little  creature  begins 
or  ends.  The  animalcule  may  be  actually  under  the 
microscope,  and  yet  the  observer  may  not  be  aware  of 


PLATE  XIII 


(a) 


From  photo-micrographs  by] 

(b) 


[Messrs.  Path6  Fr6res 


(C) 


DAPHNIA    PULEX,  (a)  female,  (b)  male  ;   AND  (c)   CYCLOPS  WITH   YOUNG 
HATCHING   OUT 


AMCEBA.  57 

it.  If  the  insignificant  speck  be  watched,  however,  it 
will  be  found  to  move  about  and  constantly  change  in 
appearance,  assuming  some  of  the  most  grotesque  forms 
and  fantastic  shapes.  These  changes  have  become  so 
well  known  that  when  masses  of  cells  of  higher  animals 
exhibit  similar  variations  of  form  they  are  called  amce- 
boids.  Among  the  amceboids  are  the  leucocytes,  or  white 
corpuscles  of  the  human  blood. 

It  is  because  the  Amoeba  changes  its  shape  so  often  and 
assumes  so  many  varieties  of  form  that  it  was  named 
Proteus  animalcule  by  Rozel  von  Rosenhof,  who  dis- 
covered it  in  1755.  In  Greek  mythology,  Proteus 
was  an  "  old  man  of  the  sea,"  who  looked  after  the  seal 
flocks  of  Neptune.  He  had  a  great  reputation  as  a 
prophet,  and  possessed  the  gift  of  endless  transformation, 
adopting  all  manner  of  shapes  and  disguises  in  order  to 
escape  from  those  inquiring  people  who  wished  to  make 
him  prophesy  for  them.  The  name  Proteus  animalcule 
was  changed  to  Amibe  by  Bury  St.  Vincent ;  and  the 
present  name,  Amceba,  is  the  corresponding  name  in 
Greek,  and  means  "  change." 

Towards  the  centre  of  the  Amceba  is  a  nucleus,  filled 
with  granular  particles,  and  often  showing  one  or  more 
bubble-like  objects,  called  the  vacuoles.  Although  this 
nucleus  does  not,  as  a  rule,  alter  in  appearance,  it  moves 
with  every  change  of  shape  in  the  Amceba  (c,  Fig.  24). 
Amceba  reproduces  itself  by  division,  one  cell  dividing 
into  two  (b,  Fig.  24).  Before  this  division  takes  place, 
however,  the  nucleus  splits  up  into  two  portions,  each 
ot  which  contains  half  the  parent  nucleus.  In  some 
cases  it  takes  only  fifteen  minutes  for  this  to  be  accom- 

(2,084)  8 


58  THE  MICROSCOPE. 

plished,  and  it  is  thus  possible  to  watch  the  entire  process 
in  the  microscope. 

Amcebce  move  about  in  a  curious  way,  for  they  are  not 
provided  with  limbs,  and  have  therefore  to  press  them- 
selves along.  This  they  do  by  putting  forth  pseudopodia, 
a  word  derived  from  the  Greek  pseudos,  "  false,"  and 
pous,  "  foot."  A  protrusion,  like  a  minute  finger,  is 
first  pushed  out  from  some  part  of  the  body  of  the 
Amoeba.  Substance  from  the  body  is  then  transferred 
to  it.  As  soon  as  the  transfer  is  completed,  another 
protrusion  is  put  out,  and  the  Amoeba  is  thus  able  to 
draw  its  body  forward  or  backward,  moving  in  any 
direction. 

As  it  moves  thus  from  place  to  place  the  tiny  crea- 
ture picks  up  its  food,  encountering  small  particles  of 
vegetable  matter,  or  occasionally  a  diatom.  These  enter 
through  any  part  of  its  body  and  mix  with  its  sub- 
stance (a,  Fig.  24). 

Amoeba  may  rightly  be  counted  among  our  most 
wonderful  animals,  for,  as  Professor  Huxley  has  said,  it 
walks  without  legs,  eats  without  a  mouth,  and  digests 
without  a  stomach  ! 

III. 

Some  animalcules  exist  in  many  kinds  of  vegetable 
infusions,  and  are  therefore  called  infusory  animalcules. 
The  great  microscopist,  Ehrenberg,  divided  them  all 
into  two  kinds  :  Poly  gastric  ("  many-stomached  ")  and 
Rotifer  ous. 

Of  the  Polygastrica  a  typical  example  is  the  beautiful 
Paramcecium  Aurelia,  which  moves  through  the  water 


PARAMOECIUM.  59 

in  constant  search  for  its  prey  (3,  Plate  X.).  It  is 
strange  that  this  magnificent  animalcule  should  be 
found  in  the  dirtiest  and  filthiest  of  ponds,  but  it  is  a 
fact  that  it  loves  best  the  kind  of  pond  which  is  a  recep- 
tacle for  the  bodies  of  dead  cats  and  dogs.  Here  it  does 
great  work  in  clearing  away  the  filth  and  refuse,  and  so 
prevents  it  destroying  the  life  of  higher  animals  and 
human  beings.  Paramcecium  is  of  an  oblong  shape  and 
covered  all  over  with  cilia.  It  is  very  active  indeed, 
darting  rapidly  backward  and  forward,  here  and  there, 
or  suddenly  turning  round  and,  by  a  quick  move- 
ment, changing  direction  altogether.  In  its  inside  we 
can  see  several  spots,  and  an  interesting  experiment 
may  be  performed.  If  we  mix  a  little  colouring  matter, 
say  carmine  or  indigo,  with  the  water  in  which  Para- 
mcecium is  confined,  we  shall  soon  see  that  the  spots 
in  its  inside  become  similarly  coloured.  This  is  due 
to  the  animalcule  taking  in  the  coloured  water,  and 
its  inside  becoming  stained  with  it.  From  this"  experi- 
ment Ehrenberg  came  to  the  conclusion  that  the  spots 
were  stomachs;  and  as  similar  spots  are  very  common 
amongst  these  animalcules,  that  is  the  reason  he  called 
the  species  "  the  many-stomached."  It  is  now  thought, 
however,  that  these  spots  are  not  true  stomachs,  but 
spaces,  or  vacuoles,  in  the  animalcule's  body. 

The  second  kind  of  infusory  animalcule,  the  Rotifera, 
are  so  called  because  with  the  microscope  they  appear 
to  have  little  wheels  on  the  upper  part  of  their  bodies. 
Their  name  comes  from  the  Latin  rota,  "  a  wheel,"  and 
few,  "  I  bear."  For  this  reason  they  are  sometimes 
called  "  wheel  animalcules."  The  so-called  wheels  are 


60  THE  MICROSCOPE. 

really  two  extended  portions  of  the  animalcule's  body, 
the  edges  of  which  are  covered  with  a  large  number  of 
cilia.  These  cilia  are  moving  incessantly,  and  thus 
cause  the  impression  of  a  tiny  wheel  rotating  on  an  axis. 

One  of  the  commonest  wheel  animalcules  is  Rotifer 
vulgaris,  found  on  the  leaves  and  stems  of  almost  any 
common  water  plant  (2,  Plate  X.).  A  more  interest- 
ing member  of  the  family  is  Melicerta,  the  brick-building 
Rotifer  (i,  Plate  X.).  It  is  also  found  on  water 
plants,  and  to  the  unaided  eye  looks  like  a  little  twig 
or  stump  about  ^j-  inch  in  length,  fixed  to  the  plant 
stem  by  one  end  of  its  body.  In  the  microscope,  the 
little  stump  is  seen  to  consist  of  numbers  of  rounded 
pellets  like  minute  bricks,  and  placed  in  regular  rows 
one  above  the  other.  As  we  watch  the  little  tube  of 
bricks,  we  are  sure  to  see  before  very  long  the  head  of 
Melicerta  peep  cautiously  above  the  edge.  Suddenly, 
as  though  assured  that  the  coast  is  clear,  Melicerta 
fearlessly  thrusts  out  its  head,  which  then  expands  and 
looks  not  unlike  a  minute  silver  pansy.  The  edges  of 
the  petal-like  lobes  of  the  head  are  surrounded  with 
innumerable  cilia,  always  in  rhythmical  motion.  When 
watching  it  under  the  microscope,  it  is  most  difficult 
to  believe  that  the  lobes  are  not  actually  two  minute 
toothed  cog-wheels,  rapidly  rotating. 

On  further  study,  Melicerta  is  seen  to  be  composed  of 
transparent,  fleshy  matter  with  many  folds.  At  one 
side  is  a  pair  of  hooked  spines,  while  at  the  other  are  two 
slender  projections.  Below  the  four  petal-like  lobes  is 
a  kind  of  chin,  immediately  beneath  which  is  the  ap- 
paratus with  which  Melicerta  makes  the  bricks  for  its 


PLATE  XIV 


from  a  photo-micrograph  by] 


(a) 


[A.  E.  Smith 


From  phucoimcrographs  by] 


[E.  Cuzner,  F.K.M.S. 


(0 


SECTIONS    OF    PLANTS 
(a)  Rattan  cane.      (b)  Stem  of  Ruscus.      (c)  Marram  grass 


THE  BRICK-MAKING  ROTIFER.  61 

"  house."  The  material  for  the  bricks  consists  of 
matter  gathered  from  the  surrounding  water  and  brought 
within  reach  of  the  brick-making  apparatus  in  currents 
set  up  in  the  water  by  the  vibrating  cilia.  The  particles 
so  gathered  may  be  seen  whirling  around  the  petal-like 
lobes  in  the  currents  they  set  up.  They  are  passed 
down  narrow  grooves  on  each  side  of  the  chin,  already 
referred  to,  until  they  reach  the  brick-making  apparatus. 
This  is  in  the  form  of  a  minute  hemispherical  cup,  which 
acts  as  both  mixing  chamber  and  mould.  The  particles 
are  here  welded  together  and  form  a  tiny  brick,  which 
is  then  placed  on  the  rim  of  the  tower  by  Melicerta 
bending  forward  its  head  and  depositing  the  brick  there. 
Brick  after  brick  is  thus  placed  in  position,  and  the 
tower  rapidly  increases  in  height. 

An  interesting  and  beautiful  experiment  may  be 
performed  with  Melicerta  by  adding  to  the  water  in 
which  it  is  working  a  little  carmine  colouring  matter. 
This  is  taken  in  with  the  particles,  and  the  resulting 
brick  is  of  a  red  colour.  The  colouring  matter  in  the 
water  may  be  changed  at  will,  and  it  is  thus  possible 
to  cause  Melicerta  to  build  a  tower  of  different  coloured 
bands,  the  width  of  each  band  depending  on  the  length 
of  time  during  which  Melicerta  is  allowed  to  work  in  the 
water  containing  any  particular  colouring  (4,  Plate  X.). 

IV. 

If  some  hay  be  steeped  in  a  glass  of  water  for  a  few 
days,  a  number  of  beautiful  little  animalcules,  called 
Vorticellce,  will  be  almost  certain  to  appear.  Some  are 
large  enough  to  be  seen  with  the  unaided  eye,  but  others 


62  THE  MICROSCOPE. 

can  only  be  examined  with  the  microscope.  You  may 
easily  distinguish  Vorticella,  because  they  have  tiny, 
cup-shaped  bodies  on  a  long  stalk,  and  look  more  like  a 
cluster  of  beautiful  microscopic  lilies-of-the-valley  than 
a  group  of  minute  animals.  If  the  slide  on  which  they 
are  placed  be  jarred,  or  if  the  little  creatures  be  otherwise 
disturbed,  the  stalk  contracts  into  a  spiral,  drawing  the 
cup-shaped  body  down  to  its  base  (4,  Plate  XL). 

Vorticellce  draw  their  food  into  their  mouths  by  setting 
up  currents  in  the  water.  These  currents  are  caused  by 
the  constant  movements  of  the  cilia,  with  which  the 
mouth  of  the  tiny  cup  is  surrounded.  The  currents  of 
water  pass  into  the  body  of  the  animalcule  by  means  of 
a  minute  aperture,  and  pass  out  again  by  a  similar  but 
different  aperture.  Many  interesting  changes  may  be 
noticed  in  the  Vorticella,  which  sometimes  become  de- 
tached from  their  stalks,  the  cup-like  body  rolling  about 
free  in  the  water  with  contracted  mouth  (7,  Plate  XL). 

Another  common  and  well-known  infusory  animalcule 
is  Stentor,  the  "  Trumpet-animalcule,"  found  attached  to 
the  under-side  of  duckweed  in  fresh  water  (i,  Plate  XL). 
It  is  generally  of  a  brilliant  green  colour,  and  is  com- 
paratively large.  When  fully  extended  it  may  measure  ^ 
inch  in  length.  In  appearance  it  resembles  the  mouth  of 
a  cornet,  or  bugle,  and  is  a  very  beautiful  object.  Its 
wide,  trumpet-like  mouth  is  fringed  with  long  cilia.  It 
reproduces  by  dividing  into  two. 

V. 

Another  interesting  Rotifer  which,  like  Melicerta,  is  also 
a  tube-dweller,  is  Stephanoceros  Eichwnii  (Plate  XII.)- 


STEPHANOCEROS.  63 

It  has  a  transparent  tube,  or  body,  resembling  gelatine, 
inside  which  may  be  seen  differently  coloured  objects. 
Some  of  these  are  the  internal  organs,  and  others,  per- 
haps, are  animalcules  which  have  been  swallowed 
and  upon  which  Stephanoceros  feeds.  Occasionally 
clusters  of  eggs  may  be  seen,  for  these  Rotifers  multiply 
in  a  similar  way  to  Daphnias — described  in  the  next 
chapter — the  eggs  being  hatched  before  leaving  the  body 
of  the  parent.  It  is  most  interesting  to  watch  the 
development  of  the  young  Stephanoceros,  which,  from 
the  time  of  its  birth  to  full  growth,  occupies  from  five 
to  ten  days. 

You  will  readily  understand  that  Stephanoceros  is  an 
exceedingly  difficult  object  to  draw,  when  I  tell  you  that 
most  of  the  existing  illustrations  of  it  are  incorrect.  Mr. 
Martin  Duncan,  F.R.M.S.,  searched  the  library  of  the 
Zoological  Society  for  illustrations  for  this  book,  and  he 
believes  that  no  good  illustration  exists.  Some  years 
ago  Mr.  Duncan  succeeded  in  taking  an  instantaneous 
photo-micrograph  of  it,  however,  and  this  photograph 
he  kindly  placed  at  the  disposal  of  my  friend  Mr.  Fisher- 
Jones,  who  has  made  the  very  beautiful  drawing  shown  in 
Plate  X.,  the  details  of  which  may  be  taken  as  being 
substantially  correct. 

The  magnificent  appearance  of  Stephanoceros  is  due 
to  the  five  curved  arms  which  protrude  above  it,  forming 
a  figure  resembling  a  delicate  arch  or  dome.  These 
curved  arms  may  be  likened  to  the  tentacles  of  an 
octopus,  for  with  them  Stephanoceros  catches  and  retains 
its  prey.  They  are  furnished  with  fifteen  rows  of  short, 
vibrating  cilia,  and  may  be  withdrawn  into  the  tube  at 


64  THE  MICROSCOPE. 

will.  This  generally  happens  if  the  creature  receives  a 
shock  from  the  jarring  of  the  microscope  stage  or  the 
plant-stem  to  which  it  clings. 

Unfortunately,  Stephanoceros  is  not  very  common.  It 
should  be  looked  for  on  the  under-surface  of  aquatic 
plants,  such  as  the  water-lily.  Specimens  once  having 
been  obtained  may  be  kept  alive  in  the  aquarium,  and 
under  favourable  circumstances  will  thrive  and  multiply. 
They  should  be  kept  in  water  obtained  from  the  pond  in 
which  they  were  found. 


PLATE  XV 


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CHAPTER  VI. 
DAPHNIA  AND  CYCLOPS. 

I. 

A  LTHOUGH  the  subjects  of  this  chapter  are  micro- 
/Iscopic  animals  and  therefore,  strictly  speaking, 
should  have  been  included  in  the  previous  chapter,  I  am 
sure  you  will  not  mind  me  giving  them  a  chapter  to  them- 
selves, for  they  are  sufficiently  interesting  to  warrant  it, 
as  I  think  you  will  agree  after  you  have  studied  them. 
If  we  have  spent  any  length  of  time  collecting  desmids 
and  other  similar  objects  at  a  pond,  we  cannot  fail  to 
have  noticed  some  of  the  comparatively  large  forms  of 
animal  life  there.  I  do  not  mean  frogs  and  newts,  but 
the  microscopic  crabs,  or  water-fleas,  and  that  curious 
looking  object  called  Cyclops,  the  one-eyed. 

The  celebrated  Dr.  Johnson  once  defined  the  word 
"  insect  "  as  meaning  "  anything  small  and  contempt- 
ible," but  this  is  by  no  means  the  definition  of  the  word 
to-day.  Science  has  stepped  in,  and  an  insect  is  now  more 
definitely  denned.  At  the  first  glance  we  might  almost 
assert  that  the  water-flea  (Fig.  25)  is  an  insect,  but  it  is 
not  truly  so,  for  it  does  not  conform  to  those  characteristic 
features  by  which  insects  are  recognized.  Although  it 

(2,084)  66  9 


66  THE  MICROSCOPE. 

may  seem  very  similar  in  appearance  to  a  flea,  Daphnia 
pulex,  the  water-flea,  belongs  to  that  class  of  animals 
called  Crustaceans.  These  have  their  soft  bodies  pro- 
tected by  an  outer  crust  or  shell,  and  the  crab  and  the 
lobster  are  larger  specimens  of  the  same  order.  There 


itennae 


Heart 

Ovary 

-Brood.  Chamber 


Maxillary 
Gland 


FIG.  25. — Daphnia,  the  water-flea. 

are  many  other  members  of  this  interesting  family, 
some  of  the  members  of  the  lower  orders  living  only  as 
parasites.  These  are  in  many  cases  so  different  from  the 
higher  members  that  they  do  not  appear  to  bear  any 
resemblance  to  them.  It  is,  nevertheless,  a  fact  that 
whether  they  live  on  land — as  do  the  centipedes  and  the 


THE  WATER-FLEA.  67 

multipedes — or  live  in  water — as  the  water-flea  and  the 
brine-shrimps — all  once  belonged  to  the  same  original 
stock. 

Daphnia  belongs  to  a  sub-division  of  Crustacea  with  the 
rather  long  name  of  Entomostracans,  meaning  shelled 
insects.  This  name  is  likely  to  be  confusing  unless  we 
keep  well  before  us  the  fact  that  these  creatures  are  not 
truly  insects.  The  true  flea  is  an  insect  having  head, 
thorax,  and  abdomen,  but  Daphnia  has  its  head 
encased  in  a  shell  and  has  no  neck,  so  that  its  head 
and  thorax  are  not  separate  but  run  into  one  another. 
The  difference  will  be  clearly  seen  by  comparing  to- 
gether a  and  b,  Plate  XIIL,  and  Plate  XXXIV.  It 
does  not  breathe  through  tracheae  or  breathing  tubes, 
but  has  numerous  legs  with  gill-like  appendages. 
Because  these  leg-appendages  are  to  Daphnia  what 
lungs  are  to  us — or  gills  to  a  fish — this  tiny  water- 
flea  may  be  said  to  breathe  through  its  toes !  Water- 
fleas  have  an  ancient  line  of  ancestors,  for  they  have 
been  traced  back  to  the  Coal  Age — that  period  of 
the  Earth's  history  during  which  our  coal  was  formed. 
In  those  far-off  times  water-fleas  must  have  lived  in 
large  numbers  in  the  great  standing  pools  of  the  coal 
forests. 

Daphnia  has  a  body  covered  with  an  almost  trans- 
parent casing,  like  that  of  a  shrimp.  Although  the  name 
of  their  sub-division  means  shelled  insects,  their  covering 
cannot  be  truly  described  as  a  shell.  It  is  composed  of 
chitine  (pronounced  "  ki-tin  "),  a  name  which  comes 
from  a  Greek  word  meaning  "  a  tunic  or  outer  dress." 
Chitine  is  indeed  a  wonderful  substance,  for  it  is  found 


68  THE  MICROSCOPE. 

in  the  insect  world  in  an  endless  variety  of  forms  and 
shapes.  The  hard  black  bodies  of  beetles  are  composed 
of  it ;  as  are  the  downy  wings  of  the  butterfly  ;  the  facets 
of  insects'  eyes ;  the  tendons,  legs,  hair,  membranes,  and 
many  other  parts  of  their  bodies. 

Through  the  transparent  shell  of  the  water-flea  may  be 
seen  the  internal  organs  at  work.  They  furnish  a  wonder- 
fully interesting  sight,  including  a  curious  organ  which 
pumps  like  a  heart,  and  many  canal-like  veins  and 
arteries.  If  the  specimen  is  a  female  it  may  be  possible 
to  see  also  numerous  eggs.  If  one  has  sufficient  patience 
these  may  be  watched  until  they  hatch  out. 

Unlike  birds,  which  first  lay  and  then  hatch  their  eggs 
in  their  nests,  Daphnia  both  lays  and  hatches  her  eggs 
inside  her  body,  and  for  this  a  special  receptacle  is  pro- 
vided by  Nature,  called  the  brood-pouch.  Here  the 
eggs  remain  until  the  little  animals  are  hatched.  Even 
then  they  are  not  cast  out  into  the  waters  to  fend  for 
themselves,  but  are  kept  inside  until  they  have  grown 
old  enough  to  swim  about  and  obtain  an  independent 
livelihood.  The  brood-pouch  is  open  to  the  surrounding 
water,  which  enters  through  a  slit  in  the  shell,  behind 
the  tail.  The  eggs  are  prevented  from  floating  out  before 
their  time  by  a  slender  tongue-like  projection,  fixed  to  the 
back  of  the  mother.  When  the  young  are  sufficiently 
grown  to  take  their  place  in  the  world  their  mother  has 
only  to  depress  her  body  a  little  more  than  ordinarily,  and 
the  door  is  open,  the  young  sliding  from  the  brood-pouch 
into  the  open  water,  like  little  ships  just  launched.  As 
is  often  the  case  with  crustaceans,  the  young  Daphnias 
are  quite  unlike  the  parent.  At  first  their  body  appears 


PLATE  XVI 


From  photo-micrographs  by] 


SECTIONS    OF    MAHOGANY 
(a)  Longitudinal  section.      (b)  Transverse  section 


THE  WATER-FLEA.  69 

like  the  bowl  of  a  miniature  spoon,  being  transparent  and 
ending  in  two  points  carrying  many  bristle-like  hairs. 
The  large  dark  eye  can  be  clearly  seen  in  front,  and  three 
pairs  of  swimming  feet,  jointed  and  bristled,  project 
stiffly  on  either  side. 

The  body  of  Daphnia  is  divided  into  five  segments, 
each  of  which  has  attached  to  it  a  pair  of  leaf-like  swim- 
ming feet.  From  the  head  there  branch  two  pairs  of 
plumed  appendages,  which  are  the  antennae.  This 
word  comes  from  the  Latin,  and  means  "  horns  or 
feelers."  Daphnia  has  only  one  eye,  which,  looking 
very  bright  and  inquisitive,  is  really  a  single  cluster  of 
ocelli,  or  insect  eyes. 

Daphnias  may  be  found  in  large  numbers  in  many  pools 
and  ditches,  coming  to  the  surface  in  the  mornings  and 
evenings  or  in  cloudy  weather,  but  seeking  the  depths  of 
the  .water  during  the  heat  of  the  day.  They  swim  by 
taking  short  springs,  darting  through  the  water  in  a 
succession  of  jerks,  and  this  is  another  reason  why  they 
have  been  called  water-fleas.  The  males  are  usually 
smaller  than  the  females  and  certainly  much  more  scarce, 
being  rarely  met  with  before  the  end  of  summer. 

Daphnias  have  many  enemies,  for  they  are  tasty  food 
for  several  other  inhabitants  of  the  water  in  which  they 
live.  It  has  been  said  on  good  authority  that  Loch 
Leven  trout  owe  their  superior  sweetness  and  richness 
of  flavour  to  their  food,  which  consists  of  small  shell- 
fish and  these  Entomostracea. 


70  THE  MICROSCOPE. 

II. 

Another  interesting  species  of  this  same  order  is  Cyclops 
(Fig.  26).  Cyclops  is  not  at  all  particular  as  to  whether 
it  lives  in  the  clearest  streams  or  in  the  muddiest  and 
most  stagnant  pools.  It  may  be  seen  like  an  animated 
atom — it  is  not  much  more  than  TV 
inch  in  length — scuttling  here  and  there 
by  a  rapid  succession  of  short  leaps 
among  the  water  weeds.  Cyclops  has 
only  one  eye,  and  that  is  how  it  gets  its 
name,  for  in  classical  mythology  the 
Cyclops  were  a  wild  race  of  giants  led  by 
their  one-eyed  chief  Polyphemus,  whose 

FIG.  '^.-Cyclops.      single  eye  WaS  Placed  ^  the  middle  °f 

his  forehead.  You  have  perhaps  read  the 
story  of  how  Ulysses  was  wrecked  off  the  coast  of  Sicily, 
and  confined  in  a  cave  by  Polyphemus,  and  of  how  he 
contrived  to  escape  by  making  the  monster  drunk  and 
burning  out  his  single  eye — so  large  that  it  required  five 
heroes  to  "  grind  the  pupil  out  " — by  a  red-hot  stake  of 
olive  wood. 

The  eye  of  tiny  Cyclops  is  placed  similarly  in  the  middle 
of  its  forehead  and  glares  like  a  minute  ruby.  It  is  so 
small,  however,  that  it  cannot  be  touched  with  the  point 
of  the  finest  needle  ;  it  is  nevertheless  of  very  elaborate 
construction,  consisting  of  a  number  of  simple  eyes. 

Cyclops  has  four  pairs  of  swimming  feet,  and  one 
rudimentary  pair.  It  also  has  two  pairs  of  antenna. 
Both  feet  and  antenna  are  covered  at  each  of  their  many 
joints  with  tufts  of  feathery  plumes.  Its  body  is  pear- 


CYCLOPS.  7i 

shaped,  broad  in  front  and  tapering  behind,  and  is  soft 
and  gelatinous.  This  body  is  divided  into  two  distinct 
parts,  the  thorax  and  abdomen.  A  jointed  shell  forms 
a  buckler  which  almost  entirely  encloses  the  head  and 
thorax.  The  abdomen  is  slender  and  might  be  mistaken 
for  the  tiny  creature's  tail.  The  tail  is  at  the  extremity 
of  the  abdomen,  however,  and  has  numerous  plume- 
like  tufts. 

On  either  side  of  the  abdomen  of  the  female  is  an  oval 
bag  or  sac,  joined  to  the  body  by  a  very  slender  thread, 
reminding  one  of  John  Gilpin,  when,  as  the  poem  says, 

"  He  hung  a  bottle  on  each  side 
To  keep  his  balance  true." 

These  oval  bags  are  packed  very  full  with  clear  and 
transparent  globules,  which  are  the  eggs.  Not  only  are 
the  eggs  thus  exposed  to  the  action  of  the  water  as  neces- 
sary, but  they  are  also  protected  from  being  destroyed 
by  the  enemies  of  Cyclops.  The  eggs  are  first  developed 
in  the  body  of  the  mother,  in  a  gland  called  the  ovary. 
When  they  are  sufficiently  matured  they  are  transferred 
into  the  oval  sacs,  through  the  exceedingly  slender  tube 
connecting  them  to  the  body.  They  are  then  carried 
about  by  the  mother  until  they  are  hatched,  when  the 
young  Cyclops  emerge  in  dozens  (c,  Plate  XIII.).  The 
sacs,  being  no  longer  required,  become  detached  and 
decay. 

Cyclops,  while  not  so  much  of  an  acrobat  as  Daphnia, 
is  nevertheless  a  very  active  creature.  It  swims  not  only 
with  its  legs  and  tail,  but  also  strikes  the  water  vigorously 
with  all  its  limbs  and  antenna.  By  rapidly  moving 


72  THE  MICROSCOPE. 

its  feet  a  whirlpool  is  created  in  the  surrounding  water 
and  minute  animals  of  various  kinds  are  thus  brought 
to  its  mouth.  Cyclops  is  sometimes  a  cannibal,  however, 
for  it  has  been  known  to  devour  even  its  own  young 
brought  in  by  the  whirlpool. 

Both  Daphnia  and  Cyclops  belong  to  the  Branchio- 
poda,  or  "  gill-footed  "  order.  There  are  several  other 
interesting  members  which  you  may  sometimes  find  in 
ponds  and  streams.  These  include  Artemia  salina, 
or  the  brine-shrimp,  found  in  salt  marshes  and  in  reser- 
voirs at  places  such  as  Lymington,  where  brine  is  de- 
posited previous  to  boiling.  It  has  peculiar  movements, 
for  in  addition  to  being  able  to  swim  in  the  correct 
position  it  can  also  swim  on  its  back  or  sides  by  means 
of  its  tail,  its  feet  being  also  in  constant  motion. 


PLATE    XVTT 

g?pB^- 


From  photo-micrographs  by]  (b)  [A.  Flatters 

LONGITUDINAL    SECTIONS    OF    WOOD 
(a)  Common  pine.       (b)  Vascular  bundle  of  Pteris  Aquilina 


CHAPTER  VII. 
PLANT    LIFE. 

I. 

NO  objects  for  microscopic  examination  are  more 
easily  obtained  than  plants.  A  few  minutes  in  the 
fields  or  meadows  will  enable  us  to  gather  material 
sufficient  for  many  hours'  observations  at  home.  The 
study  of  plant  life,  or  Botany,  is  a  very  extensive 
one,  and  includes  the  study  of  vegetable  cells  and 
tissues.  We  have  already  seen  that  all  living  things, 
whether  animals  or  plants,  consist  of  cells,  and  that 
some  consist  only  of  a  single  cell,  like  the  desmids,  while 
others  in  a  higher  stage  of  development  consist  of  a 
collection  or  assemblage  of  cells,  joined  together  (see 
Plate  XIV.),  just  as  a  house  consists  of  a  number  of 
separate  bricks  cemented  together  with  mortar.  An 
elaborately  formed  tree  is  composed  of  exactly  the  same 
kind  of  material  as  the  simplest  plant.  Those  objects 
which  consist  of  only  a  single  cell  are  said  to  be  uni- 
cellular, while  those  consisting  of  many  cells  are  multi- 
cellular  in  composition.  In  studying  the  plant  cell  we 
are  beginning  at  the  lowest  rung  in  the  study  of  life  itself. 
Plant  cells  were  discovered  about  a  hundred  years 

(2,084)  73  10 


74  THE  MICROSCOPE. 

ago.  The  early  workers  had  some  peculiar  theories  about 
their  behaviour.  For  instance,  it  was  at  one  time  be- 
lieved that  the  walls  of  the  cell  were  its  most  important 
part — that  they  were  indeed  the  cell  itself.  It  was  also 
thought  that  the  cell  contents  were  merely  food  for  the 
cell  walls,  and  that  in  those  cases  where  the  cells  were 
empty  the  contents  had  been  digested  or  assimilated  by 
the  cell  walls.  Later  it  was  discovered  that  the  contents 
of  the  cell  are  actually  of  far  greater  importance  than 
the  walls,  and  that  the  cell  walls  did  not  feed  on  the  cell 
contents.  It  was  also  found  that  the  cause  of  some  cells 
being  empty  was  due  to  the  fact  that  the  contents  of 
the  cell  had  dropped  out,  or  had  been  accidentally  shaken 
out,  when  the  specimen  was  being  prepared  for  observa- 
tion under  the  microscope. 

The  contents  of  vegetable  cells  was  first  recognized  in 
*835  by  the  French  naturalist  Dujardin,  who  described 
the  substance  as  being  formed  of  a  greyish,  semi-trans- 
parent material  of  a  slimy  nature.  In  1846  this  jelly-like 
substance  was  named  "  protoplasm  "  by  the  botanist 
Hugo  von  Mohl.  The  word  protoplasm  comes  from  the 
Greek  proton,  meaning  "  first/'  and  plasma,  "  formed 
substance/'  Protoplasm  is  often  stained  by  different 
coloured  dyes  by  microscopists,  for  by  these  means  it  is 
rendered  more  easily  visible. 

II. 

If  we  make  a  section  of  some  plant,  or  vegetable — by 
cutting  off  a  thin  slice  with  a  razor  or  sharp  knife — and 
examine  it  with  the  microscope,  we  see  at  once  that  it  is 
composed  of  minute  hollow  bodies.  Often  their  arrange- 


PLANT  CELLS. 


75 


ment  is  symmetrical  and  very  pleasing,  as  in  the  case  of 
rattan  cane  (a,  Plate  XIV.)  and  of  many  flower  buds. 
If  the  substance  be  placed  in  water  for  a  few  days  until 
it  becomes  decomposed,  these  hollow  bodies  will  separate 
and  their  different  forms  will  then  be  clearly  seen.  They 
are  the  plant  cells  of  which  we  have  been  speaking,  and 
are  generally  of  a  round  nature.  They  are  also  found 
in  other  forms,  such  as  oval  or  star- 
shaped.  Occasionally  they  lose  their 
cell-like  shape  entirely  and  appear  as 
spirals,  and  are  thus  difficult  to  recog- 
nize as  cells  (Fig.  27).  The  cells  of 
some  plants  are  pressed  closely  to- 
gether, but  others  are  loosely  packed. 
Cells  of  the  latter  kind  are  to  be  found 
in  most  pulpy  fruits. 

If  we  examine  the  cells  of  a  thin 
section  from  some  soft  fruit  like  an 
apple,  we  find  that  in  the  interior  of 
each  is  a  central  spot,  or  nucleus  (a, 
Fig.  28).  It  is  from  these  nuclei  that 
the  cells  originate.  New  cells  are  born 
from  a  similar  nucleus,  or  by  the  divi- 
sion of  a  thin  membrane  in  the  centre 
of  the  cell.  This  membrane  takes  the  place  of  the 
nucleus  and  is  called  the  "  primordial  cuticle."  Cells 
thus  formed  are  either  free  like  those  in  the  illustration, 
or  are  packed  closely  together.  In  the  latter  case  they 
are  said  to  form  a  tissue. 

When  a  section  of  a  fruit  is  made  in  which  the  cells  are 
pressed  together  equally  and  on  all  sides,  the  cells  are 


a      if      c 

FIG.  27. — Plant  ves- 
sels, (a)  Spiral, 
from  leaf-stalk  of 
rhubarb.  (&)  The 
same,  unrolled,  (c) 
Ring-like,  from  root 
of  wheat. 


76  THE  MICROSCOPE. 

seen  to  be  hexagonal  in  shape.  Such  cells  may  be  seen 
in  the  pith  of  most  plants  and  especially  in  the  common 
elder  (b,  Fig.  28).  Another  type  of  cell  is  the  stellate  or 
star-shaped  found  in  most  water-plants,  such  as  the  com- 


a  C 

FIG.  28.— Vegetable-cells,     (a)  Apple,     (b)  Elder,     (c)  Rush. 

mon  rush  or  sedge  (c,  Fig.  28).  As  will  at  once  be  seen, 
these  stellate-shaped  cells  allow  a  large  quantity  of  air 
to  be  admitted  in  the  spaces  between  the  cells,  and  the 
plant  is  thus  made  more  buoyant  and  better  adapted 
for  growth  in  water  or  marshy  places. 

III. 

The  skin  or  thin  membrane  covering  our  bodies  and  that 
of  the  bodies  of  animals  is  called  the  epidermis.  If  the 
leaf  of  any  plant  be  examined,  a  similar  thin  layer  or 
outer  skin  will  be  seen  ;  this  is  also  called  the  epidermis 
or  cuticle.  It  is  made  up  of  minute  cells,  and  varies  in 
form  in  different  plants.  Scattered  over  the  surface  of 
this  epidermis  are  curious  little  apertures  or  pores. 
These  are  the  stomata,  a  Latin  word  meaning  "  little 
mouths/'  Through  them  the  plant  breathes — for  plants 
require  to  breathe  just  as  animals  do,  though  the  process 


PLATE  XVIII 


From  a  photo-micrograph  by] 

! 


From  a  photo-micrograph  by] 


(b)  [A.  E.  Smith 

(a)  SPIRAL   VESSELS    FROM    RHUBARB,     (b)  SECTION    OF   COAL, 
SHOWING    FOSSIL    ROOTS    AND    STEMS 


STOMATA.  77 

is  not  effected  by  the  same  means.  When  we  "  breathe 
in  "  we  inhale  oxygen  into  our  lungs,  and  when  we 
"  breathe  out  "  we  exhale  carbon  dioxide.  Our  lungs 
have  extracted  the  oxygen  they  needed  and  sent  back 
the  poisonous  carbon  dioxide,  for  which  they  have  no 
use.  Plants  are  differently  constituted,  however,  for 
they  actually  need  the  carbon  dioxide  which  we  cannot 
use.  This  is  fortunate,  as  is  also  the  fact  that  plants 
give  out  oxygen  during  the  hours  of  daylight,  for  they 
thus  help  to  purify  the  air. 

The  stomata  are  generally  found  to  be  minute  oval 
openings,  having  at  each  side  a  crescent  or  kidney- 
shaped  guard-cell  which,  by  opening  or  closing,  regulates 
the  amount  of  air  admitted  to  the  leaf  (Plate  XV.). 
Stomata  are  well  seen  in  the  leaf  of  the  hyacinth,  for  in 
this  plant  the  cells  of  the  epidermis  are  transparent,  and 
the  stomata  filled  with  green  colouring  matter.  Stomata 
are  found  to  be  most  abundant  on  the  lower  side  of  leaves  ; 
indeed,  on  some  plants  they  are  only  found  there.  They 
vary  in  size  in  different  plants.  In  water-cress,  for 
instance,  they  are  very  small,  and  the  cells  of  the  epi- 
dermis are  not  straight  like  those  of  the  hyacinth  but 
sinuous,  winding  about  like  a  river. 

Just  as  the  stomata  vary  in  size,  so  too  do  they  vary 
in  number  in  different  plants.  It  has  been  estimated  that 
the  under-surface  of  leaves  of  the  hydrangea  have  160,000 
stomata  to  the  square  inch.  In  leaves  which  float  on  the 
surface  of  the  water  the  stomata  are  found  on  the  upper 
surfaces  only.  Those  leaves  which  live  entirely  sub- 
merged in  water  have  no  stomata. 


78  THE  MICROSCOPE. 

IV. 

When  cells  retain  their  original  shape  the  tissue  they 
form  is  called  "  cellular.''  But  when  the  cells  become 
elongated,  or  unite  together  forming  an  elongated  tube, 
the  tissue  thus  formed  is  called  "  vascular."  The  interior 
of  vascular  tissue  may  be  plain  or  marked  by  dots  or 
pores. 

In  the  ribs  of  leaves  and  the  stems  of  plants  elongated 
fibres  are  seen  lying  side  by  side.  These  may  also  be 
observed  in  a  longitudinal  section  of  wood  (a,  Plate  XVI.). 
This  appearance  is  called  "  ligneous  or  woody  tissue," 
and  of  it  are  composed  nearly  all  wood  and  the  more 
woody  parts  of  plants.  The  object  of  woody  formation 
in  plants  is  to  furnish  a  support  for  the  plant.  When 
this  support  is  once  formed  the  cells  of  which  it  is  com- 
posed do  not  take  any  further  share  in  the  growth  of 
the  plant.  They  do,  however,  help  to  convey  fluid  from 
the  roots  upwards  through  the  stem  and  branches  to 
the  leaves. 

Large  open  tubes  are  observed  in  the  transverse  sections 
of  most  plants  which  look  like  circular  openings  in  the 
section  and  are  called  "  ducts  "  (b,  Plate  XVI.).  Those 
which  are  marked  with  pores — as  in  the  case  of  deal, 
for  example — are  called  "  dotted  ducts."  They  are 
formed  by  deposits  in  the  interior  of  the  tube  and  are 
found  in  great  variety. 

The  cone-bearing  or  fir  tribe  of  plants  have  a  well- 
known  marking  of  the  vascular  tissue,  called  "  glandular 
woody  tissue."  In  the  case  of  the  common  pine  tree, 
for  instance,  little  circular  discs  are  seen,  each  having 


SPIRAL  CELLS.  79 

a  black  dot  in  its  centre  (a,  Plate  XVII.).  These  may 
be  observed  easily  by  making  a  thin  longitudinal  section 
of  a  piece  of  wood.  If  a  drop  of  water  be  placed  on  the 
section  the  circular  discs  will  be  more  clearly  seen. 

V. 

If  we  bend  and  break  the  stem  of  a  strawberry  leaf  we 
find  that  the  two  pieces  are  held  together  by  a  number  of 
delicate  threads  of  a  spiral  nature.  These  spiral  vessels 
are  found  in  the  stems  and  leaves  of  many  plants,  and 
resemble  in  some  cases — rhubarb,  for  instance — long 
compressed  springs  (a,  Plate  XVIII.).  Occasionally 
the  continuity  of  the  spiral  is  broken,  or  even  only  a  ring 
of  thread  remains  to  mark  the  place  where  the  complete 
spiral  would  have  been.  When  this  is  the  case  the  ring- 
like  vessels  are  called  "  annular."  Annular  vessels  are 
easily  found  in  the  leaves  of  garden  rhubarb,  or  in  the 
roots  of  growing  wheat  (c,  Fig.  27).  Yet  another  form 
of  spiral  vessels  is  that  found  in  the  roots  and  stems  of 
ferns.  Here  the  vessel  is  found  in  a  many-sided  form, 
and  because  of  its  ladder-like  appearance  is  known  as 
"  scalarif orm  tissue"  (b,  Plate  XVII.).  Not  only  do 
the  spiral  cells  give  lightness  and  elasticity  to  a  leaf  or  a 
stem,  but  they  also  act  as  trachea  for  the  breathing  organs, 
keeping  the  air  passages  open,  just  as  the  spiral  wire 
inside  a  garden  hose-pipe  keeps  it  from  "  kinking." 

If  a  thin  transparent  section  of  a  piece  of  the  bark  of 
a  plant  be  examined  under  the  microscope  its  structure 
may  be  studied.  Outside  is  the  epidermis  or  cuticle — 
corresponding  to  the  bark  of  a  tree — and  below  are  two 
layers  of  cellular  tissue,  the  innermost  layer  of  which 


8o  THE  MICROSCOPE. 

is  clearly  seen  to  be  woody  tissue.  The  outer  cellular 
layer  of  some  trees  is  very  fully  developed  and  is  known 
as  cork.  Cork  is  obtained  from  the  bark  of  an  oak  tree 
grown  principally  in  the  Levant  and  in  Portugal.  This 
cellular  structure  of  cork  may  be  plainly  seen  in  a  very 
thin  section,  the  cells  being  of  a  square  shape  and  often 
pitted. 

VI. 

Ages  ago,  in  what  is  called  the  Carboniferous  period  of 
the  Earth's  history,  the  world  was  in  a  very  different  state 
to  that  in  which  we  know  it  to-day.  The  atmosphere  was 
saturated  with  water  vapour,  the  rainfall  was  very  heavy, 
and  the  climate  was  a  great  deal  warmer  than  at  the 
present  time.  The  air  contained  a  large  amount  of 
the  poisonous  gas  carbon  dioxide,  the  plants  and  trees 
grew  very  fast,  and  because  of  the  great  quantities  of 
water  were  soft  and  juicy.  In  this  manner  a  sort  of  vast 
swampy  jungle  came  into  existence,  perhaps  not  unlike 
the  dense  mangrove-swamps  which  now  fringe  the  coast 
of  Florida.  Pine  trees,  ferns,  and  giant  horse-tails  grew 
alongside  club  mosses  fifty  feet  in  height,  and  six  feet 
in  diameter.  These  masses  of  vegetation  lived  and  died 
and  became  covered  with  deposits  of  sand  and  mud. 
The  pressure  of  these  deposits  became  so  great  that  the 
trees  and  leaves  were  pressed  flat,  forming  layers  of 
material  several  feet  thick.  This  pressure,  coupled  with 
the  internal  heat  of  the  Earth  which  partly  baked  this 
material,  continued  until  in  due  time  the  trees  and 
vegetation  were  transformed  into  coal. 

Not  only  have  we  learned  these  facts  concerning  the 


PLATE    XIX 


Starch  grains  from  a  potato 


COAL.  81 

origin  of  coal  from  the  fossil  trees  and  plants  found  in  the 
coal  measures,  but  we  know  of  them  also  because  if  a 
thin  section  of  coal  be  examined  in  the  microscope  it 
shows  the  material  to  be  of  vegetable  origin.  (Notice 
the  similar  appearance  of  b,  Plate  XVI.,  and  b,  Plate 
XVIII.) 

Coal  is  a  somewhat  difficult  object  to  examine  under 
the  microscope,  and  to  enable  us  to  see  its  construction 
in  detail  we  must  have  a  very  thin  section.  This  may 
be  obtained  by  fastening  a  suitable  piece  to  a  glass  slide 
with  Canada  balsam,  and — when  this  has  set  firmly — 
rubbing  the  coal  down  on  a  fine  stone,  until  it  is  thin 
enough  to  be  satisfactorily  examined.  From  such  a 
section  we  find  that  coal  shows  both  cellular  and  vascular 
tissue.  The  latter  tissue  is  of  the  glandular  woody 
variety,  and  from  this  fact  we  learn  that  the  trees  or 
plants  which  formed  the  coal  belonged  to  the  cone- 
bearing  or  fir  family.  This  inference  is  fully  borne  out 
by  the  remains  of  these  trees  and  plants  which  have  been 
preserved  in  the  coal  measures. 

VII. 

We  have  dealt  with  the  outside  forms  of  plant  tissues, 
and  we  are  now  to  learn  something  of  the  cell  contents. 
Here  we  find  veritable  store  chambers  where  may  be  seen 
secretions  of  starch,  sugar,  gum,  oils,  and  of  colouring 
matter.  If  the  cells  of  the  growing  parts  and  roots  of 
plants  be  examined  under  the  microscope  a  number  of 
round  grains  are  to  be  seen.  These  are  particularly 
abundant  in  the  tubers  of  a  potato  and  in  wheat,  corn, 
and  other  cereals.  In  a  section  of  a  potato  the  grains 

(2,084)  1 


82  THE  MICROSCOPE. 

may  be  seen  lying  in  the  cells  of  which  the  potato  is 
composed  (a,  Plate  XIX.).  If  a  solution  of  iodine  be 
made  up  by  adding  five  grains  of  iodine  and  five  grains 
of  iodide  of  potassium  to  an  ounce  of  distilled  water,  and  if 
a  drop  be  applied  to  the  potato  cells,  the  rounded  granules 
will  at  once  become  a  beautiful  deep  blue  in  colour.  This 
proves  that  they  are  starch,  for  no  other  substance  will 
change  to  blue  in  this  way  when  iodine  is  applied. 

Granules  of  starch  are  found  in  some  part  or  other  of 
most  plants,  and  they  are  of  many  sizes  and  shapes. 
The  starch-grains  of  wheat  are  rounded  and  of  different 
sizes  (b,  Plate  XIX.).  Those  of  the  oat  may  be  recognized 
by  the  fact  that  the  small  granules  stick  together  in 
globular  forms,  which  when  broken  up  give  place  to  very 
irregular  grains  (c,  Plate  XIX.).  The  largest  known 
starch-grains  are  those  of  arrowroot  called  Tous-les-Mois 
(a,  Plate  XIX.).  As  in  the  case  of  the  starch-grains  of 
the  potato,  these  grains  look  as  though  they  consisted 
of  numbers  of  plates,  laid  one  upon  the  other,  and 
decreasing  in  size  towards  the  top.  Often  a  small  black 
irregular  spot  is  seen  towards  the  centre  of  the  grains. 
The  starch  of  Indian  corn  has  a  peculiar  marking  like 
a  dark  cross  at  the  centre  of  each  grain  (b,  Plate  XIX.). 
Sago  and  tapioca  are  good  objects  for  examination,  as 
they  consist  almost  entirely  of  starch  (c,  Plate  XIX.). 

Often  in  examining  leaves  and  stems  with  the  micro- 
scope we  come  across  numbers  of  minute  objects  em- 
bedded in  the  plant.  They  are  found  in  the  cell  cavities 
of  many  plants,  and  also  may  be  seen  in  the  white  milky 
juice  from  the  dandelion  and  in  the  juice  of  the  common 
hyacinth.  These  are  raphides,  a  name  derived  from  the 


RAPHIDES.  83 

Greek  word  raphis,  meaning  "  a  needle/'  Indeed  the 
raphides  do  look  like  bundles  of  minute  needles,  lying 
side  by  side  (a,  Fig.  29).  They  vary  in  size  from  ^  to 
ToViy  inch,  and  are  really  deposits  of  insoluble  salts  in 
the  fluids  of  the  plant. 

Rhubarb  raphides  consist  of  oxalate  of  lime,  a  mineral 
found  in  many  other  plants  (c,  Fig.  29).  Raphides  are 
most  abundant  in  rhubarb,  especially  in  Turkey  or 
Russian  rhubarb,  and  sometimes  they  are  so  numerous 
that  if  the  root  be  chewed  it  seems  quite  gritty.  Raphides 


a 


FIG.  29. — Raphides.  (a)  From  hyacinth,  (b)  Bundle  contained  in  a  cell 
from  leaf  of  aloe,  (c)  From  stalk  of  rhubarb,  (d)  From  outer  coat 
of  an  onion. 

are  also  found  abundantly  in  the  bulbs  of  the  hyacinth 
(a,  Fig.  29),  tulip  and  onion  (d,  Fig.  29),  and  in  the 
apple-tree,  lime,  ash,  elm  ;  in  the  husks  of  rice,  wheat, 
and  in  other  grains.  Sometimes  they  occur  in  all  parts 
of  the  plant — in  the  wood,  pith,  bark,  root,  leaves, 
sepals,  petals,  fruit,  and  even  in  the  pollen.  Raphides 
have  been  formed  artificially  by  placing  cells  of  rice- 
paper  which  recently  have  been  filled  with  lime-water  in 
a  weak  solution  of  oxalic  acid.  The  artificial  raphides 
thus  formed  exactly  resembled  the  natural  raphides  of 
rhubarb. 


84 


THE  MICROSCOPE. 


VIII. 

In  most  plants  the  epidermis  or  cuticle  is  smooth, 
and  apart  from  the  features  already  described  has  few 
other  points  to  interest  us.  In  some  plants,  however, 
the  cuticle  forms  projections  called  papilla  or  warts 


FIG.  30. — Plant-hairs,  (a)  Rudimentary  hair  from  pansy,  (b)  Simple 
hair  from  common  grass,  (c)  Star-shaped  hair  from  hollyhock. 
(d)  Hair  from  throat  of  pansy,  (e)  Many  jointed,  tapering  hair 
from  common  groundsel.  (/)  Star-shaped  hair  from  lavender  leaf. 
(g)  Beaded  hair  from  pimpernel,  (h)  Glandular  hair  from  tobacco 
leaf,  (i)  Warty-surfaced  hair  from  verbena,  (j)  Hair  from  leaf  of 
chrysanthemum. 


(*',  Fig.  30).  Sometimes  also  there  are  glands,  prickles, 
or  hairs  to  be  examined.  Papilla  are  minute  swellings, 
and  consist  of  one  or  two  cells  only.  Warts  are  larger 
and  of  a  harder  nature.  The  glands  contain  secretions ; 


PLATE  XX 


rrom  a  photo-micrograph  byj 

THE    "STING"    OF    A   NETTLE 


[A.  Flatters 


PLANT-HAIRS.  85 

the  prickles  are  stiff  and  sharp,  and  the  hairs  are  long 
and  of  numerous  varieties.  In  the  pansy  is  found  an 
example  of  papilla  which  may  be  considered  to  be  a 
rudimentary  hair  (a,  Fig.  30).  There  are  also  in  the 
same  flower  others  which  are  longer  and  more  closely 
resemble  true  hairs.  Others  again  are  yet  longer,  and 
present  the  appearance  of  a  knotted  branch,  due  to  the 
sides  of  the  hair  having  drawn  together  (d,  Fig.  30). 
Simple  hairs  may  be  found  on  many  grasses,  such  as 
wheat,  barley,  and  oats  (b,  Fig.  30).  The  hairs  of  ground- 
sel are  composed  of  several  cells,  each  of  which  has  a 
separate  nucleus  (e,  Fig.  30).  The  pimpernel  has  hairs 
resembling  a  string  of  beads  (g,  Fig.  30),  while  those  of 
the  chrysanthemum  leaf  are  branched  and  resemble 
the  letter  T  (/,  Fig.  30).  Star-like  hairs  are  found  on  the 
under-surface  of  the  leaf  of  the  hollyhock  (c,  Fig.  30), 
and  branched  star-like  hairs  are  found  covering  lavender 
(/,  Fig.  30). 

Plants  belonging  to  the  same  species  have  similar 
kinds  of  hairs,  so  it  is  quite  possible  to  identify  a  species 
of  plant  by  examining  only  the  hairs  of  its  leaves.  For 
instance,  the  hairs  of  the  tobacco  plant  are  very  char- 
acteristic, for  they  terminate  in  a  knob  (h,  Fig.  30), 
and  the  quality  of  tobacco  may  be  tested  by  the  presence 
of  these  hairs.  Though  tobacco  leaf  may  be  imitated 
and  the  mixture  adulterated,  it  is  impossible  to  imitate 
the  peculiarities  of  these  microscopic  hairs. 

Some  plants  have  hairs  with  glandular  cells,  which 
secrete  oily  or  resinous  matter.  The  leaves  of  the  stinging 
nettle  are  a  well-known  example,  for  the  hairs  have  glands 
containing  an  irritant  fluid  at  their  roots.  The  ends  of 


86  THE  MICROSCOPE. 

these  hairs  terminate  in  an  extremely  fine  point,  so 
delicate  that  it  is  broken  off  by  the  slightest  touch,  and 
the  poisonous  fluid  flows  out,  entering  our  flesh  and 
causing  the  "  sting  "  (Plate  XX.). 


CHAPTER  VIII. 
FLOWERS. 

I. 

FLOWERS,  beautiful  though  they  always  are  even 
without  any  optical  aid,  appear  much  more  so  in 
the  microscope.  The  wonders  of  their  construction,  the 
marvellous  delicacy  of  their  minute  parts,  and  their 
gloriously  beautiful  colouring  are  a  thousand  times  more 
wonderful  when  magnified.  Petals,  sepals,  stamens,  and 
pistils  all  have  a  story  to  tell,  and  only  await  the  coming 
of  the  botanist  to  lay  this  bare. 

Grasses  furnish  us  with  many  examples  of  minute 
flowers,  which  are  revealed  in  all  their  beauty  under  the 
microscope.  The  tiny  floret  of  the  meadow-grass,  for 
instance,  exhibits  stamens  covered  with  pollen,  and 
feathery  stigmas  attached  to  a  minute  ovary.  The  lily- 
of-the-valley — a  larger  flower  than  that  of  meadow-grass 
— is  of  triplet  structure,  and  is  of  great  beauty.  The  leaf, 
even  to  the  unaided  eye,  shows  parallel  veins,  and  the 
single  seed  chamber,  if  examined  carefully  and  in  detail, 
will  furnish  much  interesting  information. 

Among  the  most  interesting  of  flowers  are  the  orchids, 
of  which  many  thousands  of  species  are  known.  They 

87 


88  THE  MICROSCOPE. 

are  more  common  in  the  tropics  than  in  our  northern 
latitudes,  and  many  have  been  the  exciting  adventures 
of  orchid  hunters.  You  may  have  read  accounts  of  their 
exploits  in  more  than  one  book.  Some  of  the  exotic 
or  foreign  orchids  have  been  successfully  cultivated  in 
England  by  imitating  the  natural  conditions  of  heat 
and  moisture  of  the  forests  of  the  Amazon,  of  India, 
and  of  other  countries.  We  ourselves  may  not  be  so 
fortunate  as  to  be  able  to  examine  any  of  these  exotic 
species,  but  we  may  look  for  some  of  the  more  lowly 
members  of  the  great  family  which  grow  wild  in  this 
country.  For  instance,  in  June  and  July  the  spotted 
orchis  is  found  in  chalk  and  limestone  districts.  The  bee 
orchis  and  the  fly  orchis  suggest  the  peculiar  shape  these 
flowers  take. 

In  the  case  of  most  flowers,  the  beautifully  marked 
tissue  of  which  they  are  composed  is  worthy  of  examina- 
tion. Spiral  fibres,  such  as  have  already  been  described, 
may  be  found  also  in  these  cells.  The  fibres  are  well  seen 
in  the  anthers  of  the  furze,  while  in  the  dead  white  nettle 
they  are  found  growing  in  an  irregular  manner.  In  the 
anthers  of  the  narcissus  the  cells  are  almost  completely 
annular,  and  look  like  a  number  of  disconnected  rings. 
Yet  another  form  is  that  of  the  star-shaped  fibres  of  the 
crown  imperial  which  radiate  from  a  central  point. 

The  cone-bearers,  the  pines  and  firs,  also  present  many 
objects  of  interest — the  peculiar  fibre-like  appearance 
of  the  cones,  the  cellular  construction  of  the  "  pine- 
needles,"  and  the  resinous  juices  often  found  oozing  from 
their  branches.  The  catkin-bearing  trees — such  as  the 
willow,  birch,  and  alder — have  curious  flowers  and  seed 


PLATE  XXI 


. 


THE  COMPOSITES.  89 

vessels,  which  abound  with  microscopic  objects.  So  too 
do  the  members  of  the  highest  order  of  dicotyledons,  the 
Ranunculacea,  or  rose  family.  These  include  the  fruit 
trees — such  as  plum,  apple,  cherry — and  all  flowers 
which  resemble  a  rose  in  their  structure. 

Such  flowers  as  the  daisy  and  the  dandelion  are  not 
single  flowers  like  the  buttercup  and  the  rose.  When 
magnified  they  are  at  once  seen  to  be  colonies  of  flowers, 
that  which  we  call  the  daisy  being  really  made  up  of  a 
number  of  very  small  flowers.  These  flowers  belong  to 


FIG.  31. — Section  of  a  daisy. 

the  Composite^,  the  composite  or  compound  flowers. 
Cut  through  the  flower-head  of  a  daisy  and  you  will  see 
the  yellow  florets  are  quite  separate  and  resemble  small 
bell-shaped  tubes  (Fig.  31).  When  matured  or  fully 
grown  they  show  two  tiny  stigmas  outspread.  Inside 
the  tube  of  the  floret  is  a  ring  of  stamens,  with  their 
pollen  cases  or  anthers  lying  side  by  side,  forming  a  tube 
enclosing  the  pistil  and  lying  within  the  floral  tube  itself. 
This  anther  tube  is  a  distinctive  feature  of  the  flowers  of 
the  family  to  which  the  daisy  belongs. 

The  white  florets  outside  the  yellow  are  not  so  numerous 

(2,084,1  12 


90  THE  MICROSCOPE. 

as  the  latter,  but  are  more  conspicuous  by  their  shape  and 
size.  They  attract  insects,  just  as  do  the  markings  and 
similar  features  on  other  flowers,  directing  them  to  where 
the  nectar  is  secreted.  The  white  floret  has  a  short 
tube  with  a  long  blade-like  ending  (Fig.  31).  A  pistil 
with  two  stigmas  may  be  seen  in  the  tube,  but  no  stamens 
exist.  The  pistil  is  not  affected  by  pollen,  and  therefore 
does  not  produce  any  seeds,  the  work  of  reproduction 
being  accomplished  by  the  yellow  florets. 

II. 

Whenever  possible  collect  and  examine  pollen  grains 
from  different  flowers,  for  they  vary  in  shape  and  size, 


PIG.  32. — Pollen  grains,  i.  Heath.  2.  Hollyhock.  3.  BuUercup.  4. 
Mallow.  5.  Tulip.  6.  Rose.  7.  Iris.  8.  Clematis.  9.  Passion-flower. 
10.  Anemone,  u.  Dandelion.  12.  Auricula.  13.  Primrose.  14.  Hazel. 

each  species  of  plant  having  its  own  particular  form. 
It  would  be  interesting  for  every  possessor  of  a  micro- 
scope to  study  all  these  different  appearances,  recording 


POLLEN  GRAINS.  91 

in  an  observation  book  the  varying  features  of  each, 
and  perhaps  giving  a  rough  sketch  of  the  pollen  grains 
described. 

The  pollen  grains  of  many  plants  are  oval  (5,  6,  etc., 
Fig.  32).  Those  of  the  hazel  are  triangular  (14,  Fig.  32) ; 
those  of  the  heath,  three-lobed  (i,  Fig.  32).  Those  of 
the  dandelion,  and  of  many  other  plants  of  the  Com- 
positecz  order,  are  beautifully  sculptured  (n,  Fig.  32), 
while  the  grains  of  the  passion-flower  are  engraved  with 
three  rings  (9,  Fig.  32).  Those  of  the  hollyhock  and 
mallow  are  covered  with  sharp-pointed  spines  and  look 
like  miniature  pin-cushions  (2  and  4,  Fig.  32).  These 
projections  enable  the  minute  grains  to  more  easily 
hold  fast  to  surfaces  on  which  they  are  cast. 

All  these  pollen  grains  are  actual  plant  cells,  and  their 
purpose  is  to  be  carried  to  the  pistil  to  fertilize  the  young 
ovules  which  form  the  seeds  of  the  plant  and  from  which 
young  plants  grow. 

III. 

The  microscope  has  shown  us  exactly  how  the  fertiliza- 
tion of  flowers  takes  place.  In  this  great  work  insects, 
and  particularly  bees,  are  prominently  concerned.  Some 
flowers,  like  those  of  the  grasses  and  the  common  hazel, 
are  fertilized  by  the  wind,  but  the  majority  of  flowers 
depend  upon  insects  for  the  accomplishment  of  this 
all-important  operation. 

Let  us  try  to  understand  exactly  what  takes  place 
in  fertilization  and  why  it  is  necessary.  To  enable  us  to 
study  this  matter  we  will  choose  a  daffodil  about  which 
to  speak,  for  this  flower  is  both  a  good  example  and 


92  THE  MICROSCOPE. 

easily  obtainable.  We  know  that  the  daffodil  is  made  up 
of  "  flower-leaves  "  and  that  there  is  no  calyx  as  in  the 
case  of  the  primrose.  The  corolla  is  a  deep  yellow  tube, 
and  to  it  the  flower-leaves  are  joined.  If  we  cut  the  flower 
in  two,  down  the  centre,  we  find  there  is  a  long  rod  which 
is  called  the  style  (b,  Plate  XXIIL).  At  the  end  of  this 
there  is  a  sticky  knob,  the  stigma.  Six  smaller  rods 
are  grouped  round  the  style,  and  these  are  called  the 
stamens.  They  are  thickened  at  the  end  near  the  stigma, 
these  thickenings  forming  the  anthers.  The  anthers  are 
the  pollen-bearing  parts  of  the  flower,  and  though  the 
position  of  each  often  varies  you  will  find  both  anthers 
and  stigma  in  nearly  every  kind  of  flower. 

Below  the  corolla  of  the  daffodil  is  the  ovary,  the 
chamber  where  the  seeds  are  formed.  In  the  ovary  we 
can  see,  with  the  naked  eye,  a  number  of  round  objects 
of  a  transparent  nature.  These  are  the  ovules,  and  in  the 
course  of  time  they  may  become  seeds.  There  is,  how- 
ever, a  remarkable  difference  between  the  ovule  and  the 
seed.  If  we  planted  one  of  the  former  it  would  never 
grow  into  a  plant,  but  would  simply  wither  away  and 
decay  in  the  ground.  On  the  other  hand,  if  we  set  a 
seed,  sooner  or  later  it  would  spring  up  and  become 
a  plant  resembling  that  from  which  the  seed  was 
taken. 

An  ovule  only  becomes  a  seed  after  being  fertilized, 
and  this  is  accomplished  by  some  pollen  being  placed  on 
the  stigma.  The  style  is  a  kind  of  tube  connected  with 
the  ovary.  When  the  grains  of  pollen  reach  the  stigma 
they  adhere  to  it,  because  it  is  viscid,  or  sticky.  The 
viscid,  sugary  secretion  with  which  it  is  covered  stimulat- 


PLATE  XXII 


From  a  drawing  by]  ^Ellison  Hawks 

POLYCYSTINA 


FERTILIZATION. 


93 


ing  the  pollen  grains  to  growth,  causes  them  to  sprout 
and  send  out  long  shoots  called  pollen  tubes.  These 
pollen  tubes  grow  down  the  style, 
forcing  their  way  between  its  cells 
(Fig.  33).  They  often  attain  an  ex- 
traordinary length,  sometimes  extend- 
ing for  several  inches. 

The  cells  of  the  style  also  contain 
a  sugary  liquid,  and  these  further 
nourish  the  growth  of  the  pollen 
tubes,  which  ultimately  reach  the 
ovary  where  the  ovules  are  found. 
Each  ovule  has  a  minute  opening 
called  the  micropyle,  or  "  little  gate," 
and  here  the  pollen  tube  enters. 
Having  done  this  it  pours  into  the 
ovule  nutrition  from  the  pollen  grain 
above,  the  ovule  undergoes  certain 
important  changes — called  fertiliza- 
tion— and  then  becomes  a  true  seed. 


tion  of  stigma. 


IV. 


Just  as  the  pollen  grains  form  an  interesting  study,  so 
too  do  the  seeds  of  plants,  and,  as  in  the  case  of  the  former, 
they  vary  in  form  and  size  in  different  plants.  As  we  have 
seen,  after  the  ovule  has  been  fertilized  it  becomes  a  seed, 
containing  the  embryo  or  young  plant.  In  many  plants 
the  seed  is  sufficiently  large  to  be  seen  by  the  unaided 
eye,  but  the  microscope  will  undoubtedly  reveal  new 
features  of  interest.  The  seed  is  covered  with  an  outer 
membrane,  called  the  "testa,"  and  in  some  cases  this 


94 


THE  MICROSCOPE. 


is  often  curiously  marked.  The  seed  of  a  red  poppy,  for 
instance,  is  kidney-shaped,  and  has  peculiar  reticular 
markings  (a,  Fig.  34).  The  seed  of  black  mustard  is  of 
a  more  circular  shape,  and  its  surface  is  covered  with  a 
delicate  network  of  fine  lines  (b,  Fig.  34).  The  seed  of  the 
snap-dragon  is  covered  with  irregular  ridges,  and  granular 
markings  (c,  Fig.  34).  A  somewhat  similar-looking  seed 


a 


FIG.  34. — Plant-seeds,    (a)  Red 
(c)  Snapdragon.     ( 


i       (b)  Black  mustard, 
ckweed. 


to  that  of  the  mustard  is  the  chickweed,  which  is  covered 
with  numerous  blunt  projections  and  resembles  a  minute 
clove-ball  (d,  Fig.  34). 

In  some  plants  the  seeds  adhere  to  the  fruit,  which  is 
often  incorrectly  called  the  seed.  Among  these  are  the 
aniseed,  dill,  and  carraway.  Some  of  the  fruits  of  these 
plants  are  covered  with  minute  hooks, 


CHAPTER  IX. 
FUNGI  AND  MOULDS. 

I. 

OFTEN  when  walking  in  the  country  we  see  mush- 
rooms and  toadstools  ;  sometimes,  too,  beautifully 
coloured  fungi  are  noticed  on  or  near  trees.  Although 
all  these  are  well  known  to  belong  to  the  fungus  family, 
there  are  many  other  members  of  the  same  family  which 
are  not  so  well  known.  It  is  not  necessary  to  walk 
into  the  country  to  find  objects  of  this  class,  for  mouldy 
cheese  will  provide  interesting  examples,  as  also  will 
decayed  portions  of  fruits  and  any  other  articles  which 
have  "  gone  mouldy." 

We  have  already  seen  something  of  one-celled  plants. 
By  far  the  greater  number  of  these  are  found  living  in 
rivers,  streams,  or  ponds.  Some,  however,  exist  on  moist 
rocks  or  on  old  walls.  One  of  these  is  "  Gory  Dew  " 
(Palmella  cruenta),  which  is  of  very  simple  structure 
indeed,  consisting  simply  of  minute  globular  cells  (/,  Fig. 
35).  It  causes  a  red  stain  to  appear  on  the  surface  of 
damp  objects,  and  belongs  to  the  same  family  as  the 
red  snow  plant. 

Darwin  tells  us  in  The  Voyage  of  the  Beagle  that  during 

96 


96  THE  MICROSCOPE. 

his  passage  of  the  Cordillera  the  footsteps  of  the  mules 
in  the  snow  were  stained  pale  red,  and  a  little  of  the 
snow  rubbed  on  paper  gave  it  a  pale  red  tinge.  The  red 


f 


FlG.  35. — Fungi,  (a)  Puccinia  graminis.  (b)  Mucor  mucedo,  a  fungus 
from  mouldy  bread,  (c)  "  Cholera-fungus."  (<i)  Yeast  cells. 
(«)  Vinegar  plant.  (/)  "  Gory  Dew  "  (Palmetto,  cruenta). 

colour  was  entirely  due  to  the  presence  in  large  numbers 
of  the  tiny  plant  Pwtococcus  nivalis.  The  phenomenon, 
of  somewhat  rare  occurrence  in  this  country,  was  noticed 
in  many  places  after  a  severe  snowstorm  in  1908.  The 


PLATE  XXIII 


FUNGI.  97 

wonderful  little  plant  Protococcus  nivalis  appears  on  the 
surface  of  the  snow,  and  so  quickly  do  the  cells  reproduce 
themselves  that  an  Arctic  or  Alpine  landscape  may  be 
changed  from  white  to  red  in  a  single  night.  This  rapid 
growth  of  Protococcus  nivalis,  and  its  peculiar  red  colour, 
gave  rise  to  many  fearsome  tales  in  olden  days,  for  then 
the  true  nature  of  the  phenomenon  was  not  understood, 
it  being  thought  that  tlie  snow  was  stained  red  with 
blood. 

Examined  in  the  microscope,  Protococcus  nivalis  is  seen 
to  consist  of  numbers  of  spheres,  in  colourless  cases, 
each  no  more  than  T^^TT  mcn  in  si26-  When  perfect, 
the  spherical  cells  are  not  unlike  a  red-currant  berry. 
Minute  though  they  are,  the  cells  perform  all  the  functions 
of  growth  and  reproduction  as  completely  as  the  larger 
and  more  highly  organized  members  of  the  vegetable 
kingdom. 

There  are  many  other  members  of  the  same  family, 
one  form  attacking  bread,  and  another  potatoes.  In  each 
case  the  bread  and  potatoes  are  given  the  appearance 
of  having  been  dipped  in  blood. 

II. 

Of  similar  structure  is  the  yeast  plant,  or  fungus,  by 
the  aid  of  which  bread  is  made.  It  belongs  to  a  group 
called  Saccharomyces,  or  sugar  fungi.  Yeast  cells  furnish 
us  with  an  interesting  and  typical  example  of  the  con- 
struction of  cells,  of  their  growth  and  of  their  method 
of  reproducing  themselves.  The  cells  commence  their 
life  as  a  creamy  foam,  floating  on  the  top  of  a  brewer's 
vat.  Under  the  microscope  they  look  like  a  crowd  of 

(2,084)  13 


98  THE  MICROSCOPE. 

yellowish  grains.  Most  of  them  float  about  quite  alone, 
or  isolated,  but  here  and  there  are  some  which  are  joined 
together  in  chains,  like  beads  on  a  string.  They  resemble 
oval  globes  in  shape,  and  on  an  average  are  ^ws  mcn 
in  size  (d,  Fig.  35).  Each  is  filled  with  almost  colourless 
matter,  in  which  are  to  be  seen  one  or  more  bubble-like 
objects,  or  vacuoles. 

When  yeast  cells  are  placed  in  a  suitable  liquid — or 
fermentable  fluid,  as  it  is  called — they  grow,  or  vegetate. 
Each  cell  then  commences  to  put  out  one  or  two  pro- 
jections or  buds,  and  looks  like  a  large  potato  with  a 
smaller  one  attached.  These  projections  are  the  beginning 
of  the  young  cells,  which  are  really  offshoots.  When  they 
are  sufficiently  developed  they  become  detached  and 
break  away  from  the  parent,  forming  complete  cells. 
Later,  they  themselves  become  parent  cells  in  their 
turn,  and  in  this  manner  a  single  yeast  cell  develops  into 
chains  of  four,  five,  or  six  cells  in  the  space  of  only  a  few 
hours. 

If  the  fermentation  of  the  liquid  in  which  they  are 
placed  is  stopped,  the  cells  composing  these  chains  break 
away  and  become  detached.  So  long  as  the  cells  remain 
in  liquid  from  which  they  can  extract  food,  or  nutriment, 
the  birth  of  new  cells  will  continue.  If  the  liquid  in  which 
the  cells  are  placed  becomes  unsuitable — if,  for  instance, 
the  sugar  it  contains  be  used  up — or  if  it  becomes  dried 
up,  the  contents  of  the  cells  contract.  The  spores,  or 
seed  germs,  then  become  inactive  for  the  time  being. 
Although  they  may  become  quite  dry  to  all  outward 
appearance,  they  are  not  killed,  but  still  contain  the 
mysterious  element  life.  In  fact,  the  cells  are  not  easily 


FUNGI.  99 

deprived  of  their  living  contents  by  being  subjected  to 
either  high  or  low  temperatures,  for  as  soon  as  conditions 
are  once  more  favourable  they  revive  and  recommence 
reproducing  themselves. 

III. 

A  minute  vinegar  plant  may  be  cultivated  by  simply 
allowing  vinegar  to  stand  for  a  little  time  in  a  jar  and 
exposed  to  the  air.  At  first  the  vinegar  plant  is  seen  to 
be  composed  of  elongated  cells,  looking  like  a  collection 
of  pieces  of  finely  chopped  cotton  or  thread  (e,  Fig.  35). 

More  fully  developed  thread-like  fungi  are  often  found 
in  decomposing  fluids.  One  of  them  is  misnamed 
"  Cholera-fungus,"  which  was  at  one  time  believed  to 
be  the  cause  of  cholera  (c,  Fig.  35).  Sometimes  specimens 
of  this  fungus  may  be  obtained  by  exposing  a  piece  of 
damp  glass  or  similar  substance  to  the  air  in  a  damp 
and  unwholesome  cellar  or  room. 

It  is  believed  that  all  these  simple  fungi  are  really 
different  forms  of  the  fungus  which  produces  the  common 
mould  known  as  Muccr  mucedo.  This  mould — which  is 
found  almost  everywhere — attacks  jam,  fruit,  and  vege- 
tables, especially  those  of  a  sugary  or  starchy  nature. 
Sometimes  we  see  peaches  and  other  delicate  fruits 
wrapped  in  cotton-wool  or  tissue  paper.  The  wrap- 
ping acts  as  a  preventive  against  mould,  which  quickly 
attacks  bruised  fruits,  the  spores  obtaining  an  entrance 
to  the  fruit  through  the  openings  in  the  skin  caused  by 
the  bruises. 

If  we  carefully  collect  some  common  mould  and  examine 
it  with  the  microscope,  we  find  that  the  main  mass — 


loo  THE  MICROSCOPE. 

known  as  the  "  mycellium  " — is  composed  of  a  large 
number  of  hyphce,  or  knob-like  structures ;  they  stand 
upright,  and  each  one  terminates  in  a  round  swelling 
(b,  Fig.  35).  These  round  objects  are  the  sporangium, 
or  seed  cases,  as  they  may  be  called,  and  contain  thousands 
of  minute  oval  bodies,  named  the  endo-spores.  When 
these  are  ripe  they  burst,  and  the  spores  are  scattered  in 
all  directions  as  a  very  fine,  invisible  dust. 

Mould  is  found  almost  everywhere  where  there  are 
substances  which  are  exposed  to  damp  and  decay. 
We  find  moulds  in  our  gardens,  in  our  houses,  in  our 
food,  and  in  our  clothes.  A  form  of  mould  even  is 
often  able  to  obtain  a  sufficient  supply  of  nourishment 
to  exist  in  the  paste  of  wall-paper  and  in  old  books. 
Sometimes  moulds  look  like  spots  or  markings  on  the 
leaves  of  plants.  At  others  they  appear  as  mildew, 
smut,  or  rust.  These  latter  names  do  not  mean  the 
smut  of  the  factory  chimney,  nor  the  rust  of  old  iron ; 
they  are  the  names  given  to  moulds  because  they  closely 
resemble  these  objects  in  appearance.  The  smut  mould 
on  plants  is  a  dirty-looking  growth,  and  the  rusts  are 
growths  of  a  distinctly  reddish  colour. 

IV. 

One  of  the  most  troublesome  of  these  moulds  is  that 
called  "  corn  mildew,"  although  it  sometimes  attacks 
wheat  and  other  grasses  as  well  as  corn.  It  is  caused  by  a 
fungus  called  the  Puccinia  graminis.  This  particular  form 
of  mould  has  been  closely  studied  with  the  microscope, 
and  it  is  now  believed  that  it  commences  its  existence 
in  the  berberry  plant,  the  leaves  of  which  when  attacked 


PLATE  XXIV 


FUNGI.  101 

appear  to  be  covered  with  a  fine  red  rust.  Under  the 
microscope  these  rust-like  markings  are  seen  to  consist 
of  myriads  of  structures  resembling  minute  cups  in 
shape,  and  filled  with  orange-coloured  dust  (Fig.  36). 
This  dust  is  the  spores — or  microscopic 
seeds — of  the  fungi,  and  it  is  esti- 
mated that  each  minute  cup  contains 
no  less  than  a  quarter  of  a  million 
spores !  Later,  the  fungus  passes 
through  different  stages,  at  one  time 
having  the  appearance  shown  at  a, 

Fig.  35.  FIG.     36.  —  Cluster- 

T-I  M  t        •  i        CUDS  on  underside 

The  corn  mildew  is  so  common,  and      of  leaf, 
its  spores    so    numerous,   that   they 
mingle  with  the  seeds  of  the  grain  when  ground  into 
flour.     If  carefully  looked  for  they  may  be  found  in 
almost  any  piece  of  bread,  if  it  be  examined  under  the 
microscope. 

V. 

Fungi  often  attack  plants  and  cause  irregular  spots  to 
appear  on  their  leaves.  These  are  generally  seen  in 
summer  and  autumn,  and  may  be  of  a  yellow,  red,  or 
black  colour.  A  common  form,  and  one  much  dreaded 
in  many  parts  of  the  country,  is  the  potato  disease — as 
it  is  commonly  termed.  There  are  several  forms  of  this 
disease,  but  that  generally  met  with  is  Phytophthora 
infestans,  also  called  "  the  late  blight."  This  fungus  is 
found  wherever  the  potato  is  grown,  and  in  this  country 
generally  appears  about  July  or  August.  The  leaves  of 
the  potato  lose  their  brilliant  green  colouring,  becom- 


102  THE  MICROSCOPE. 

ing  mottled  and  patched  with  yellow.  They  gradually 
change  to  dark  brown  and  perhaps  even  to  black.  Some- 
times the  stems  themselves  are  affected. 

The  tubers,  as  the  potatoes  are  called,  accumulate 
starch  and  other  matter.  For  the  formation  of  this 
starch  they  depend  entirely  upon  the  leaves,  which  form 
it  with  the  aid  of  sunshine.  Thus,  it  is  quite  easy  to 
understand  that  if  the  leaves  are  attacked  by  the  mould, 
and  die,  the  tubers  do  not  grow  to  their  full  size.  In- 
stead of  the  potatoes  being  large  and  healthy  they  are 
much  smaller,  and  the  crop  is  diminished.  In  countries 
like  Ireland,  where  the  poorer  people  depend  for  their 
food  mainly  upon  potatoes,  it  may  be  a  very  serious 
thing  if  the  disease  attacks  the  crops. 

VI. 

Many  forms  of  fermentation  are  due  to  the  action  of 
microscopic  fungi.  There  is,  for  instance,  that  form 
which  takes  place  in  wine-making.  The  fermentation  of 
the  juices  of  the  grape — or  whatever  other  fruit  is  used — 
commences  with  the  development  of  a  minute  fungus, 
the  germs  of  which  were  already  present  in  the  fruit,  or 
in  its  skin,  when  it  was  gathered. 

The  common  drink  in  Japan  is  a  kind  of  beer  called 
saki,  and  this  is  made  by  fermenting  rice.  Another 
drink  made  by  the  Japanese  is  soy,  which  is  obtained  by 
mixing  the  beans  of  the  soja  with  an  equal  quantity  of 
roughly  ground  wheat  or  barley,  which  is  then  placed  in 
a  warm  place  to  ferment.  In  both  these  cases  the  action 
is  due  to  a  microscopic  fungus  which,  by  feeding  on 
certain  substances  in  the  mixture,  causes  a  chemical 


LICHENS  AND  MOSSES.  103 

change  to  take  place.    This  change  is  called  fermenta- 
tion. 

VII. 

There  are  also  numerous  lichens,  mosses,  and  ferns 
which  abound  with  interest  to  the  microscopist.  One 
particular  form  of  lichen,  of  a  yellow  colour,  is  often  seen 
on  railings  and  on  the  bark  of  trees.  It  resembles  pieces 
of  dried  yellow  paper,  and  is  composed  of  scales  which 
show  on  their  surface  spots  of  deeper  yellow  colour.  Cut- 
ting through  these,  we  find  a  number  of  cases,  or  asci, 
containing  the  spores. 

In  marshy  ground  the  bog-moss  Sphagnum  is  often 
found.  This  moss,  during  the  War,  was  collected  in 
many  parts  of  the  country,  for  it  forms  a  valuable 
surgical  dressing,  better  even  than  cotton-wool,  and  has 
been  largely  used  in  the  healing  of  wounds.  The  leaves 
are  a  splendid  example  of  fibre-tissue,  and  well  illustrate 
the  development  which  takes  place  in  tissue,  if  examined 
day  by  day. 


CHAPTER   X. 
MARINE  LIFE. 

I. 

IT  is  not  all  of  us  who  are  so  fortunate  as  to  live  by  the 
sea  ;  but  in  normal  times  it  is  reasonable  to  suppose 
that  most  of  us  may  visit  the  seaside  at  some  time 
or  other  during  our  holidays.  During  such  a  visit  we 
may  take  the  opportunity  of  collecting  a  quantity  of 
material  for  examination  under  the  microscope,  either 
during  some  wet  day  of  our  holiday  or  to  take  home  with 
us  for  dealing  with  at  leisure. 

Living  in  sea  water  we  find  plants  and  animals  closely 
resembling  those  of  fresh  water.  Indeed  they  belong  to 
the  same  families,  although  of  entirely  different  species. 
There  are,  for  instance,  many  forms  of  minute  seaweeds 
which  belong  to  the  same  families  as  the  diatoms  and 
the  Coniferce.  The  structure  of  the  fruit-bearing  organs 
of  the  larger  seaweeds  are  very  interesting  under  the 
microscope.  A  frond  of  "  bladder-wrack  "  shows  swollen 
masses  in  certain  places,  covered  with  rough  bodies  of 
yellow  colour.  These  contain  spores,  which  carry  deli- 
cate hairs  of  various  forms. 

104 


PLATE  XXV 


SPONGES. 
II. 


105 


There  are  also  numbers  of  minute  marine  animals 
which  are  of  the  greatest  interest  to  us.  Among  the  most 
lovely  forms  are  the  sponges,  which  are  composed  of 
animal  matter  combined  with  horn,  chalky,  or  flinty 
substance.  This  forms  a  network  which  may  be  seen  by 
cutting  with  a  pair  of  sharp  scissors  a  thin  section  from 
a  bathroom  sponge  (a,  Fig.  37) .  Other  forms  of  sponges 


FIG.  37. — Sponge  spicules.  (a)  Section  of  common  sponge,  (b)  Spicu- 
lum  from  fresh-water  sponge,  (c)  Spiculum  from  Tetkea.  (d) 
Section  of  common  British  sponge,  (e)  Spiculum  of  (d)  mag- 
nified. (/)  Pin-shaped  spiculum  from  Cliona. 

may  be  found  with  seaweed  on  the  seashore,  and  these 
show  a  network  composed  of  sharp,  needle-like  objects, 
or  flinty  spicules,  as  they  are  called  (d,  Fig.  37).  These 
spicules  lie  one  over  the  other  and  differ  in  form  and  size 
in  various  sponges.  In  fact,  so  pronounced  and  well 
known  are  their  differences  that  it  soon  becomes  quite 
easy  to  identify  the  species  of  a  sponge  from  the  shape 
of  its  spicules.  Some  spicules  are  pin-headed,  as  in  the 
case  of  Cliona,  a  little  boring  sponge,  found  in  the  shells 

(2,084)  14 


106  THE  MICROSCOPE. 

of  old  oysters  (/,  Fig.  37).  Another  well-known  spicule 
is  one  shaped  like  a  delicate  dumb-bell  and  belonging  to 
the  fresh-water  sponge  (6,  Fig.  37).  Some  spicules — as 
in  the  case  of  Tethea — are  round  and  covered  with 
pointed  projections,  reminding  us  of  part  of  a  mace,  one 
of  the  curious  weapons  of  war  in  use  in  the  olden  days 
(c,  Fig.  37) .  Sometimes  sponge  spicules  are  mounted  along 
with  diatoms  to  make  beautiful  designs ;  Plate  XXI. 
shows  two  of  these  slides.  In  a  spicules  resembling 
minute  pick-axes  alternate  with  groups  of  three  navicular 
diatoms.  In  b  the  dumb-bell  type  of  spicule  is  to  be 
seen,  and  there  is  also  another  kind,  looking  like  a  delicate 
corkscrew,  the  whole  forming  a  pleasing  figure  and  a  very 
eloquent  testimony  of  what  patience  can  do  in  the  ar- 
ranging of  microscopic  objects. 

III. 

We  must  now  leave  the  sponges  and  learn  something  of 
another  and  equally  interesting  class  of  object  found  in 
the  sea.  These  are  the  Foraminifera,  a  name  derived 
from  the  Latin  words  foramen,  "  an  aperture,"  and  fero, 
"  to  bear."  The  Foraminifera  are  simple  animalcules, 
like  the  Amoeba,  but  possessing  the  power  to  surround 
themselves  with  a  chalky  or  calcareous  shell.  These 
shells  have  tiny  holes  in  them,  and  hence  their  name, 
which  means  "  the  hole-bearers."  To  form  their  shells, 
the  little  creatures  collect  the  carbonate  of  lime  con- 
tained in  the  sea  water,  and  surround  their  bodies  with 
it.  Some  Foraminifera  construct  their  shells  of  minute 
sand  grains,  and  these  are  called  "  tests/'  Both  kinds 
of  shells  are  almost  indestructible,  and,  in  the  case  of 


FORAMINIFERA.  107 

fossil  Foraminifera,  have  lasted  through  the  ages.  Dur- 
ing this  time  they  have  often  undergone  great  pressure 
in  the  Earth's  crust,  still  remaining  unbroken  and 
perfect. 

Foraminifera  are  larger  in  size  in  the  waters  of  the 
warmer  oceans  than  they  are  in  the  waters  of  the  polar 
seas.  As  we  have  already  mentioned,  the  shells  vary 


FIG.  38. — Foraminifera. 

greatly  in  design.  Some  (like  the  kind  called  Largena) 
consist  of  a  single  chamber  and  resemble  a  small  Indian 
club  (a,  Fig.  38).  Others,  like  Globigerina,  are  a  cluster 
of  chambers  arranged  spirally  (c,  Fig.  38).  The  younger 
Globigerina  shells  number  from  eight  to  twelve  chambers, 
and  are  thin  and  smooth ;  but  the  older  shells  may  con- 
sist of  sixteen  or  even  more  chambers,  and  are  much 
thicker. 


108  THE  MICROSCOPE. 

Often  Foraminifera  may  be  found  alive  among  the 
roots  of  the  giant  seaweeds  generally  found  on  the  shore 
after  a  storm.  If  the  roots  be  washed,  and  the  water 
therefrom  be  allowed  to  stand,  the  Foraminifera  will 
sink  to  the  bottom,  and  may  then  be  picked  out  and 
examined. 

Some  Foraminifera  so  closely  resemble  the  nautilus, 
that  early  naturalists  did  actually  include  them  in  the 
same  class  of  shell-fish.  Now,  however,  it  is  well  known 
that  the  animal  bodies  of  the  two  creatures  are  quite 
distinct  from  each  other.  There  is  also  an  important 
difference.  The  nautilus,  although  it  forms  chambered 
cells,  lives  in  the  last  formed  chamber.  It  adds  a  larger 
chamber  when  the  size  of  its  body  so  increases  that  it  is 
necessary  to  give  more  room,  withdrawing  from  each 
chamber  in  succession.  The  Foraminifera  which  so 
closely  resembles  the  nautilus  in  appearance  is  not  a 
single-bodied  animal  but  has  a  composite  body,  consist- 
ing of  a  number  of  segments  connected  one  to  the  other 
by  a  filament  or  membrane.  It  continues  to  increase 
by  "  budding/'  and  as  each  new  segment  is  formed  a 
new  chamber  is  added  to  the  shell.  Thus — unlike  the 
case  of  the  nautilus — each  chamber  of  the  Foraminifera 
is  occupied  by  a  segment  of  the  animal's  body. 

IV. 

Until  forty  or  fifty  years  ago  very  little  was  known 
about  the  floor  of  the  ocean.  Some  people  knew  that 
our  oceans  were  so  deep  in  certain  places  that  the  depth 
could  be  measured  only  in  "  miles,"  but  that  was  about 
the  extent  of  our  knowledge.  Some  scientists  argued 


PLATE  XXVI 


ri 

PQ 

§ 

I 

e  a 


FORAMINIFERA.  109 

that  nothing  could  live  in  water  so  deep,  where  the  sea 
floor  was  in  total  darkness,  and  expressed  the  opinion 
that  the  pressure  of  the  water  itself  must  be  so  great  as 
to  forbid  the  existence  of  life  of  any  kind.  However, 
a  kind  of  net  and  basket  called  the  deep-sea  dredge 
was  invented,  and  with  this  the  floor  of  the  ocean 
at  its  deepest  places  was  explored.  The  dredge  was 
lowered  from  a  ship,  which  meanwhile  travelled 
slowly  along  and  dragged  the  dredge  with  it.  The 
dredge  was  then  hauled  to  the  surface  and,  to  the  wonder 
of  all,  numerous  delicate  forms  of  life  were  found  in  it. 

Among  the  multitude  of  interesting  objects  which 
the  deep-sea  dredge  reveals,  is  a  light-coloured  mud  or 
ooze.  This  ooze  is  nearly  wholly  composed  of  Foramin- 
ifera  shells,  the  largest  of  which  are  less  than  a  pin's  head 
in  size.  The  celebrated  German  naturalist  Ehrenberg 
estimated  that  one  cubic  inch  of  ooze  contained  over 
1,000,000  of  these  shells.  They  are  of  all  manner  of 
shapes,  some  having  one  chamber,  others  several.  There 
are  straight  shells,  curved  shells,  flat  shells,  round  shells, 
coiled  shells,  and  oblong  shells.  Some  are  white  and 
chalky  looking,  others  resemble  pearls,  and  others,  yet 
again,  are  clear  and  transparent  like  glass.  All  the  shells 
from  the  ocean  floor  are  empty,  for  they  are  shell-cases 
only.  If  we  scoop  up  some  of  the  tiny  shells  which 
float  on  the  surface  of  the  ocean  and  in  its  waters,  how- 
ever, we  find  they  have  living  creatures  inside. 

Foraminifera  are  found  in  greatest  numbers  in  mud 
or  ooze  dredged  up  from  the  bed  of  the  Atlantic,  but 
many  varieties  may  be  obtained  from  the  sands  around 
our  own  coasts.  They  also  live  in  rock  pools  or  attached 


no  THE  MICROSCOPE. 

to  seaweeds.  If  placed  under  the  microscope  in  some 
sea  water,  the  curious  action  of  the  pseudopods  may  be 
seen.  When  the  shells  are  to  be  mounted  on  slides  they 
must  first  be  boiled  in  a  strong  solution  of  potash  ;  this 
destroys  their  animal  contents,  but  does  not  injure  the 
shell.  The  shells  may  also  be  obtained  from  chalk 
cliffs  and  separated  by  placing  the  chalk  in  water  until 
softened. 

Foraminifera  are  divided  into  two  groups,  called 
Imperforata  and  Perforate  In  the  former  group  are 
classed  those  shells  which  have  one  main  opening  (or 
sometimes  more),  and  in  the  latter  group  the  shells 
which,  in  addition  to  the  main  opening,  have  perfora- 
tions through  the  walls. 

V. 

No  doubt  many  of  you  have  seen  the  chalk  deposits 
in  one  part  or  another  of  our  Island.  On  the  east  coast 
of  Yorkshire,  at  Bempton  and  Flamborough,  the  cliffs 
are  several  hundred  feet  high.  The  chalk  cliffs  near 
Dover  are  known  to  the  sailors  as  "  the  white  walls  of 
old  England."  London  is  built  on  chalk,  as  is  also 
Paris;  and  similar  rocks  to  these  are  found  extending 
over  France,  Denmark,  and  Central  Europe.  They 
reach  also  from  Northern  Africa  to  the  Crimea,  and  from 
Syria  to  the  Sea  of  Aral  in  Central  Asia. 

All  these  chalk  deposits  consist  largely  of  the  remains 
of  Foraminifera  shells.  When  their  inhabitants  die,  the 
shells  sink  to  the  bottom  of  the  ocean,  and  there  form 
the  fine  mud  or  ooze  to  which  we  have  already  referred. 
The  shells  are  always  falling,  as  lightly  as  motes  in  a 


FORAMINIFERA.  in 

sunbeam,  sometimes  through  thousands  of  feet  of  ocean 
depth.  It  is  just  as  if  a  continuous  snowstorm  was 
taking  place  in  the  sea,  the  flakes  of  which  are  just 
as  beautiful  when  seen  in  the  microscope  as  are  snow- 
flakes  when  similarly  viewed. 

This  rain  of  shells  is  going  on  at  the  present  time, 
and  exactly  the  same  happened  ages  ago.  Far  back  in 
the  Earth's  history  countless  millions  of  these  shells 
fell  day  and  night,  century  after  century.  Foraminifera 
inhabited  the  prehistoric  oceans,  just  as  their  descendants 
live  in  our  seas  to-day.  Every  drop  of  water  was  alive 
with  them,  and  they  were  so  numerous  that  the  floors  of 
the  oceans  in  which  they  lived  soon  became  covered 
with  their  shells.  As  they  continued  to  fall,  so  did  their 
shells  continue  to  accumulate,  until — after  the  passing 
of  many  millions  of  years,  perhaps — they  formed  the 
chalk  deposits  which  we  know  to-day.  These  deposits 
of  chalk  are  called  by  geologists  the  cretaceous  rocks, 
from  the  Latin  word  creta,  which  means  "  chalk."  The 
deposits  have  been  lifted  high  above  the  level  at  which 
they  were  formed  by  Earth  movements,  and  they  show 
us  that  in  times  gone  by  there  must  have  existed  great 
seas  where  they  occur.  For  instance,  the  cretaceous 
rocks  tells  us  that  at  one  time  South-East  England, 
France,  Germany,  Poland,  Russia,  Egypt,  Arabia,  and 
Syria  were  all  under  the  sea. 

The  stone  of  the  Pyramids  consists  of  the  fossil  shells 
of  a  variety  of  Foraminifera  called  nummulites  (Latin 
nummulus,  "  a  small  coin  "),  a  species  which,  as  its  name 
implies,  is  coin-like  in  shape. 


112  THE  MICROSCOPE. 

VI. 

Among  the  most;  beautiful  objects  which  the  microscope 
can  show  are  the  Polycystina,  a  group  of  Radiolaria 
(Plate  XXII.).  The  name  is  derived  from  the  Greek 
polus,  "  many,"  and  kustis,  "  a  cyst  or  box."  They  are 
of  all  shapes,  and  are  covered  with  minute  perforations 
through  which  the  creature  inside  could  thrust  its 
pseudopodia  and  capture  food,  or  propel  itself  through  the 
water.  If  a,  Plate  XXIII.,  be  examined  with  a  magni- 
fying glass,  some  of  the  more  common  varieties  may  be 
seen.  When  seen  on  a  dark  background  Polycystina 
look  like  miniature  jewels.  They  are  obtained  from  the 
chalky-looking  Barbadoes  earth,  which  is  sometimes  used 
for  polishing  purposes. 

VII. 

Another  interesting  animal  which  lives  in  the  sea  is 
Noctiluca  miliaris,  a  name  which  means  "  thousands  of 
nightlights."  To  this  minute  animal  is  due  the  peculiar 
phosphorescent  appearance  often  seen  in  the  sea.  De- 
scribing the  phenomenon  Darwin,  in  his  famous  book, 
The  Voyage  of  the  'Beagle,  says :  "  While  sailing  a 
little  south  of  the  Plata  on  one  very  dark  night,  the  sea 
presented  a  very  wonderful  and  very  beautiful  spectacle. 
There  was  a  fresh  breeze,  and  every  part  of  the  surface 
which,  during  the  day,  is  seen  as  foam,  now  glowed  with 
a  pale  light.  The  vessel  drove  before  her  bows  two 
billows  of  liquid  phosphorus,  and  in  her  wake  she  was 
followed  by  a  milky  train." 

Another   writer   has   described   the   phenomenon   as 


PLATE  XXVI I 


HE E DIE  fotNT 


From  photo-micrographs  by] 


(C) 


(Ellison  Hawks 


(a)  WING    OF   BEE.       (b)  STING   OF   WASP.       (c)  STING   OF   BEE 
AND    NEEDLE    COMPARED 


"  THOUSANDS  OF  NIGHT-LIGHTS."  113 

follows  :  "In  certain  oceans  and  seas,  in  calm  weather, 
when  the  nights  are  dark,  the  wake  of  the  passing  ship 
resembles  a  path  of  oscillating  gold,  increasing  in  bril- 
liancy until  it  glistens  in  whiteness.  The  contrast  with 
the  surrounding  black  waters  becomes  most  impressive. 
The  boatman  puts  off  from  the  shore,  and  as  he  dips  his 
oars  and  lifts  them  up  the  dripping  waters  sparkle  as  if 
illuminated  by  thousands  of  microscopic  arc-lamps,  while 
the  prow  of  his  boat  cuts  its  way  through  liquid  bril- 
liants. A  gentle  ripple  is  sufficient  at  certain  times  to 
cause  the  luminosity  to  appear,  but  when  the  sea  is 
absolutely  smooth  there  is  no  observable  display." 

The  peculiar  phosphorescent  light  which  Noctili4ca 
miliaris  emits  may  be  seen  even  when  only  a  com- 
paratively small  number  of  the  creatures  are  contained 
in  a  jar.  If  the  >ar  be  gently  shaken,  or  knocked,  the 
little  captives  instantly  emit  a  soft  light,  of  a  beautiful 
greenish  hue.  This  is  strong  enough  to  be  seen  even  by 
lamplight.  It  only  lasts  for  an  instant,  however,  and 
the  animals  require  a  short  rest  before  it  can  be  renewed. 

Noctiluca  miliaris  belongs  to  a  group  of  the  Protozoa, 
and  is  about  FV  inch  in  diameter.  It  can  just  be  seen 
by  the  naked  eye  if  the  water  in  which  it  is  contained 
is  held  up  to  the  light.  With  a  hand  magnifying  glass 
its  flagellum,  or  tail-like  appendage,  is  visible.  Flagellum 
is  a  Latin  word  meaning  "  a  little  whip,"  and  the  presence 
of  this  feature  dis-.inguishes  that  group  of  Protozoa  to 
which  Noctiluca  miliaris  belongs,  from  the  group  of 
which  Amoeba  is  a  typical  example.  Flagella  are  long, 
slender  filaments,  usually  few  in  number,  and  are  used 
both  for  obtaining  food  and  for  moving  about  through 

(2,084)  1§ 


H4  THE  MICROSCOPE. 

the  water.  The  former  is  accomplished  by  vibrating 
the  ftagella,  which  sets  up  currents  and  whirlpools ; 
particles  of  food  are  thus  drawn  to  the  animal's  mouth. 
The  motion  of  the  animal  through  the  water  is  accom- 
plished by  a  peculiar  lashing  movement,  which  causes 
the  animal  to  be  dragged  along  in  jerks  or  leaps. 


CHAPTER   XI. 

AN  INSECT  LABORATORY  AND  WORKSHOP: 
THE  HONEY-BEE. 

I. 

IN  this  little  book  we  have  not  sufficient  space  to 
learn  everything  about  the  many  kinds  of  insects 
and  their  varying  appearances  in  the  microscope.  In- 
stead, I  intend  to  tell  you  a  little  about  only  one  insect, 
so  that  you  may  learn  from  it  something  of  what  applies 
to  all  insects  generally.  The  insect  which  I  have  chosen 
for  the  purpose  is  Apis  mellifica,  the  honey-bee,  because 
not  only  is  it  well  known  to  all,  and  sufficiently  common 
for  specimens  to  be  easily  obtained,  but  it  is  one  of  the 
most  interesting  of  all  the  members  of  the  insect  world. 

We  cannot  here  consider  the  wonderful  story  of  hive- 
life — that  has  already  been  told  in  another  volume  of 
the  series  to  which  this  book  belongs.*  In  these  pages 
we  are  more  concerned  with  the  aspect  of  the  bee  as 
shown  by  the  microscope,  and  with  an  examination  of  the 
wonderful  limbs  and  the  parts  of  its  body  which  enable 
it  to  turn  nectar  into  honey,  and  to  manufacture  the 
wax  required  for  the  comb.  We  must  see  something  also 

*  Bees :  Shown  to  the  Children.     By  Ellison  Hawks. 
115 


n6  THE  MICROSCOPE. 

of  the  tools  with  which  it  collects  the  pollen,  builds  the 
cells,  and  accomplishes  the  numerous  other  processes 
required  of  it  in  its  daily  life. 

II. 

The  bee  is  a  typical  insect,  having  head,  thorax,  and 
abdomen.  The  head  is  something  like  half  a  split  pea 
in  shape,  with  the  rounded  part  turned  to  the  front,  and 
is  joined  to  the  thorax  by  a  thin  neck.  There  are  five 
eyes,  two  compound  and  three  simple,  and  it  will  be  as 
well  if  we  note  here  the  -difference  between  the  two  types 
of  eyes.  Spiders  possess  only  simple  eyes,  but  the  bee 
has  both  compound  and  simple,  as  I  have  mentioned. 
In  the  case  of  the  bee,  the  compound  eyes  are  placed 
one  on  each  side  of  the  head,  and  are  large  and  prominent, 
like  those  of  the  house-fly.  The  simple  eyes  are  to  be 
found  at  the  top  of  the  head,  and  are  hidden  away  in  the 
fine  golden  hairs  with  which  the  head  is  covered  (a, 
Plate  XXIV.).  The  compound  eyes  are  of  a  deep, 
purplish  colour,  and  glisten  like  satin.  They  are  made 
up  of  a  multitude  of  hexagonal,  or  six-sided,  cells  similar 
in  shape  to  those  of  the  honeycomb.  These  cells  are 
called  facets,  which  means  little  "  windows,"  and  each 
one  measures  about  ^-^  part  of  an  inch  in  diameter. 
Each  facet  is  really  a  small  eye  in  itself,  and  that  is  the 
reason  the  eyes  are  called  compound.  In  the  eye  of 
the  worker  bee  there  are  over  6,000  facets,  each  one 
pointing  in  a  slightly  different  direction.  Large  though 
this  number  appears  to  be,  it  is  less  than  half  the  number 
possessed  by  the  drone,  whose  facets  number  13,000  in 
each  eye.  The  queen-bee  has  about  5,000. 


PLATE  XXVIII 


Froai  photo-micrographs  by)  (fo) 

HOOKS   ON    WING   OF   BE! 
(a)  Unlocked.       (b)  Locked 


lEllison  Hawks 


THE  EYES  OF  THE  BEE.  117 

Each  facet  acts  as  a  minute  lens.  With  a  camera 
a  photograph  may  be  taken  of  any  object  at  which  it 
is  pointed,  for  the  lens  with  which  it  is  fitted  throws  an 
image  of  the  object  on  the  photographic  plate.  Our 
own  eyes  act  as  lenses,  and  throw  an  image  of  whatever 
we  look  at,  not  upon  a  photographic  plate,  but  upon  a 
sensitive  surface  called  the  retina,  a  Latin  word  meaning 
"  a  small  net."  The  retina  catches  the  picture  from  the 
crystalline  lens  of  our  eye  and  passes  it  on  to  the  brain, 
where  we  "  translate  "  it,  as  it  were,  and  understand  it. 
Each  facet  in  the  compound  eye  acts  as  a  minute  lens. 
At  one  time  it  was  believed  that  each  facet  made  a 
separate  image  of  the  object  at  which  it  was  directed, 
but  this  is  not  now  generally  believed  to  be  the  fact. 
It  is  realized  that  it  is  unlikely  that  Nature  would  provide 
an  eye  to  show  several  thousands  of  flowers  instead  of 
the  one  at  which  the  eye  was  directed.  It  seems  much 
more  probable  that  each  facet  forms  an  image  of  only 
that  part  of  the  object  which  is  exactly  in  front  of  it,  all 
the  pictures  combining  to  form  a  single  image,  just  as 
the  small  coloured  bricks  in  a  mosaic  work  combine  to 
form  a  pattern. 

The  simple  eyes  are  arranged  so  as  to  form  a  triangle, 
like  this  v  In  the  case  of  the  drone  the  compound 
eyes  are  so  large  that  they  extend  not  only  over  all  the 
space  at  the  side  of  his  head  but  also  right  over  the  top, 
covering  the  position  occupied  by  the  simple  eyes  in  the 
worker.  On  account  of  this  the  drone's  simple  eyes  are 
placed  lower  down  on  the  front  of  his  head,  the  position 
approximating  more  to  that  of  our  own  eyes. 

The  simple  eyes  are  so  called  because  they  do  not  seem 


H8  THE  MICROSCOPE. 

to  be  nearly  so  complicated  in  their  construction  as  the 
compound  eyes,  but  nevertheless  they  have  an  elaborate 
structure. 

Over  the  surface  of  the  compound  eye  are  distributed 
numerous  long,  straight  hairs.  Their  chief  purpose  is 
to  protect  the  facets,  just  as  the  eyelashes  of  our  own 
eyes  protect  them.  The  simple  eyes  have  tufts  of  hair, 
like  eyebrows,  surrounding  them,  but  these  are  so  placed 
that  they  do  not  interfere  with  the  range  of  vision. 
Bees  have  no  eyelids  as  we  have,  so  they  have  to  rely 
upon  these  hairs  to  protect  their  eyes  from  dust  and  other 
foreign  bodies. 

III. 

In  addition  to  the  eyes,  the  head  carries  the  antenna, 
or  "  feelers,"  as  they  are  commonly  called.  The  antenna 
of  the  worker  bee  each  consists  of  a  single  long  joint  and 
eleven  small  joints  (b,  Plate  XXV.).  The  long  joint  is 
called  the  "  scape,"  meaning  a  shaft  or  stem,  and  the 
smaller  ones  are  said  to  form  the  flagellum,  which,  as 
we  have  already  seen,  means  "  a  little  whip."  The 
antenna  of  the  drone,  whilst  resembling  those  of  the 
worker,  have  one  more  small  joint  in  the  flagellum, 
thus  making  the  total  number  twelve.  They  are  fixed 
to  the  bee's  head  by  a  cup-and-ball  joint,  and  can  be 
moved  in  practically  any  direction.  In  addition,  each 
of  the  joints  of  the  flagellum  can  be  moved  separately. 

The  scape  is  covered  with  numerous  hairs,  which  are 
both  long  and  fine.  The  first  three  joints  of  the  flagellum 
are  also  covered  with  hairs  which,  however,  differ  in 
appearance  from  those  of  the  scape,  being  much  shorter 


THE  ANTENNA  OF  THE  BEE.  119 

and  thicker.  They  look  more  like  bristles,  and  all  point 
in  a  downward  direction.  The  remaining  eight  joints 
are  covered  with  multitudes  of  still  smaller  hairs,  and 
these  again  differ  in  their  construction.  The  hairs  on 
the  antenna  of  a  drone  number  about  4,000,  and  on 
those  of  a  worker  about  28,000.  Each  hair  is  connected 
with  a  nerve  so  sensitive  that  the  most  delicate  touch 
can  be  perceived  immediately. 

The  antenna  serve  many  useful  purposes,  and  are  of 
a  wonderful  and  complicated  structure.  In  the  hive, 
although  it  is  dark,  the  bees  are  able  to  find  their  way 
about  by  means  of  them.  They  build  their  combs  with 
their  aid,  and  with  them  they  communicate  with  each 
other.  Watch  bees  on  the  alighting  board  of  a  hive, 
how  they  approach  and  gently  cross  their  antenna,  as 
two  duellists  cross  their  swords  before  a  fight.  For  a 
fraction  of  a  second  one  seems  to  lightly  tap  the  antenna 
of  the  other,  and  it  is  obvious  that  a  communication  is 
passing  between  them. 

In  the  antenna  are  the  nerves  with  which  bees  smell. 
The  "  smell  hollows,"  as  they  are  called,  are  exceedingly 
numerous  and  minute.  Each  of  the  last  eight  joints  of 
some  worker  bee's  antenna  have  fifteen  rows  of  twenty 
"  smell  hollows,"  a  total  of  over  2,400  in  each  antenna. 
The  queen  has  only  about  1,600,  but  the  drone  has 
37,000  on  each  antenna. 

Here  also  are  found  the  ears  of  the  bee.  We  generally 
expect  to  find  the  ears  of  living  creatures  in  their  heads, 
but  Nature  sometimes  plays  queer  tricks  in  the  animal 
world.  For  instance,  who  would  dream  of  looking  for 
the  ears  of  a  cricket  in  its  legs  ?  Those  of  the  grass- 


120  THE  MICROSCOPE. 

hopper  are  found  in  a  similar  place.  Then  there  is  a 
kind  of  shrimp,  called  the  Mysis,  which  actually  has  its 
hearing  apparatus  in  its  tail !  Thus,  when  we  remember 
these  peculiarities  it  is  perhaps  not  quite  so  strange  as 
it  at  first  seemed  to  find  the  bee's  ears  in  its  antenna. 
The  ears  take  the  form  of  oval-shaped  holes  or  depressions, 
and  are  quite  distinct  from  the  "  smell  hollows  "  already 
mentioned.  They  measure  only  about  T^j-J^  Part  of 
an  inch  in  size,  and  each  is  surrounded  by  a  minute  ring 
of  bright  orange  colour. 

The  central  part  of  the  antenna  is  hollow  and  contains 
the  nerves  which  run  like  a  bundle  of  electric  cables  to 
the  ganglia.  Ganglia  comes  from  the  Greek  and  means 
"  a  knot,"  and  it  is  really  a  knot  or  a  bunch  of  nerves, 
for  they  are  the  "  nerve  centres  "  situated  in  the  body. 
The  chief  ganglion  is  in  the  head,  and  corresponds  to  the 
brain  in  animals.  Other  ganglia  are  found  in  the  thorax 
and  in  the  abdomen. 

IV. 

The  tongue  of  an  insect  is  called  the  proboscis,  a  Greek 
word  meaning  a  "  front  feeder  or  trunk,"  and  indeed  the 
bee's  tongue  is  not  unlike  the  trunk  of  an  elephant  in 
appearance.  The  tongue  itself  is  long  and  tapering,  and 
is  composed  of  a  number  of  ring-like  structures,  covered 
with  hairs,  arranged  in  a  regular  manner,  and  pointing  in 
a  downward  direction  (b,  Plate  XXIV.).  In  the  tongue  of 
the  queen  and  drone  the  rows  of  hairs  number  from  sixty 
to  sixty-five,  but  in  the  case  of  a  worker,  which  has  a  much 
longer  tongue,  they  number  ninety,  to  a  hundred  rows. 
Some  of  these  hairs  are  used  for  feeling,  but  most  of  them 


PLATE  XXIX 


POISON  BAG 


THE  THORAX  OF  THE  BEE.  121 

are  necessary  for  collecting  the  nectar  from  the  flowers. 
This  adheres  to  the  hairs  when  the  bee  pushes  its  head  into 
the  corolla  and  sweeps  from  side  to  side  with  its  tongue. 
The  tongue  is  extremely  flexible  and  can  be  moved  in 
any  direction.  At  the  extreme  end  is  the  spoon,  also 
used  in  collecting  nectar,  and  covered  with  delicate 
branched  hairs  (b,  Plate  XXIV.).  The  front  is  composed 
of  maxilla,  or  inner  jaws.  The  tongue,  but  not  the  pro- 
tecting tube,  can  be  drawn  up  into  the  bee's  mouth  at 
will.  The  labial  palpi  each  consist  of  four  joints,  of 
which  the  two  nearest  the  mouth  are  the  largest.  They 
also  have  numerous  hairs,  used  for  feeling  as  well  as  pro- 
tection. 

The  maxilla,  or  inner  jaws,  have  already  been  men- 
tioned. The  outer  jaws  are  very  hard  and  have  sharpened 
edges.  The  action  of  most  insects'  jaws  resembles  a  pair 
of  scissors  in  opening  and  closing.  Those  of  the  bee  are 
very  powerful  and  are  chiefly  used  in  the  making  of  honey- 
comb, the  wax  of  which  is  thinned  out  by  their  aid. 

V. 

The  thorax,  or  chest,  of  an  insect  may  be  likened  to  the 
engine-room  of  a  ship,  for  it  is  the  centre  of  all  movement 
so  far  as  the  wings  and  legs  are  concerned.  It  is  divided 
into  three  parts  :  the  pro-thorax  or  forward  division  near- 
est the  head,  the  meso-thorax  or  middle  division,  and  the 
meta-thorax  or  after  division.  It  contains  several  large 
muscles,  for  the  bee  is  a  powerful  flier,  and  is  thickly 
covered  with  fine,  downy  hairs.  Among  these  hairs  are 
a  number  of  other  spike-like  hairs,  in  which  pollen  is 
entangled  when  the  bee  enters  a  flower. 

(2,084)  16 


122  THE  MICROSCOPE. 

The  thorax  also  contains  the  trachea,  or  air  sacs.  These 
fill  with  air  and  make  the  body  more  buoyant,  and  thus 
assist  the  flight  of  the  insect. 

VI. 

The  legs  of  the  bee  are  very  interesting,  and  nearly  every 
microscopist  is  sure  to  have  slides  of  them,  for  they  are 
well  known  as  "  show  objects/'  There  are,  of  course,  three 
pairs  of  legs,  one  pair  being  attached  to  each  division  of 
the  thorax.  Each  leg  has  nine  joints  and  terminates  in 
two  claws  and  a  kind  of  soft  pad  (c,  Plate  XXVI.).  The 
claws  are  used  in  walking  over  rough  surfaces,  and  when 
wax-making  the  bees  hang  in  chains  or  festoons  from  the 


CLAW**         PAD 

FIG.  39. — The  claw  and  pad. 

roof  of  the  hive  by  hooking  their  feet  together.  The  soft 
pad  is  called  the  pulvillus  and  is  used  for  walking  on  a 
smooth  surface  or  in  positions  in  which  the  claws  cannot 
be  used.  When  the  claws  fail  to  grip  any  surface  they 
slide  down  under  the  foot,  and  the  pad  is  thus  automatic- 
ally brought  into  action,  for  it  presses  against  the  smooth 
surface  and  adheres  to  it  by  means  of  the  viscid  moisture 
with  which  it  is  covered  (Fig.  39). 
The  legs  nearest  the  head  are  the  shortest  pair,  and 


A  BEE'S  BRUSH  AND  COMB. 


123 


their  most  interesting  features  are  the  brushes  and  comb 
(Fig.  40).  The  brushes  consist  of  hairs  which  serve  two 
purposes,  one  for  cleaning  the  comb  and  the  other  for 
freeing  the  hairs  of  the  eye  of  pollen  and  dust.  The 
comb  is  a  semi-circular  notch  around  which  are  arranged 


FIG.  40. — The  brush  and  comb. 

about  eighty  teeth.  Just  above  is  the  vellum,  a  kind  of 
hinge  or  lid,  and  so  named  because  it  "  covers  "  the 
antenna  when  it  is  drawn  into  the  comb  and  holds  it 
there  whilst  it  is  being  pulled  through.  This  operation 
is  performed  by  the  bee  bringing  its  front  leg  to  its  head 
and  then  moving  the  leg  outwards.  By  this  movement 


124 


THE  MICROSCOPE. 


the  antenna  is  drawn  into  and  through  the  comb,  the 
teeth  removing  any  dirt  and  pollen  which  may  be  adher- 
ing to  it. 

The  second  pair  of  legs  have  a  kind  of  stiff  spike  used 
for  cleaning  the  wings.  The  hindermost  pair  are  the 
longest,  and  are  furnished  with  wax-pincers  consisting 
of  a  row  of  spikes  at  the  joint  (a,  Plate  XXVI.,  and 
c,  Plate  XXIX.).  The  corbicula,  or  pollen  basket,  is 
also  found  in  the  hindermost  legs.  In  it  pollen  is  carried 
from  the  flowers  to  the  hive.  The  large  joints,  or  thighs 
as  it  were,  of  this  pair  of  legs  are  much  broader  than  the 
corresponding  joints  in  the  other  legs. 
They  are  also  hollowed  out  and  are  fur- 
nished at  the  edges  with  spikelike  hairs, 
which  curve  inwards  over  the  hollow 
(Fig.  41).  This  is  on  the  outside  of  the 
leg,  and  on  the  inside  are  several  combs, 
made  up  of  rows  of  hairs.  When  the 
thorax  is  covered  with  pollen  it  is  combed 
out  by  means  of  these  hairs  by  the  bee 
crossing  its  legs  beneath  its  body.  The 
pollen  is  then  fashioned  into  a  little 
ball  or  pellet  and  passed  into  the  pollen 
basket,  where  it  is  held  until  the  bee 
reaches  the  hive.  Pollen  is  mixed  with 
honey  to  make  "  bee-bread."  This  is 
food  for  the  young  bees. 


FIG.  41.— Pollen 
basket. 


VII. 


Bees  belong  to  the  Hymenoptera  order  of  insects,  and 
have  four  wings — a  pair  of  large  and  a  pair  of  small, 


PLATE  XXX 


(a) 


From  photo-inicrojjraphs  by] 


Co) 


[K.  Cuzner,  KK.M.S. 


SPIRACLES    OF    DYTISCUS 

(a)  Showing  the  spiracles  on  the  side  of  the  Water-Beetle,     (b)  A  highly 
magnified  spiracle 


THE  WINGS  OF  THE  BEE.  125 

called  respectively  the  anterior  and  the  posterior.  The 
name  is  derived  from  the  Greek  words  hymen,  "  marriage," 
and  pteron,  "  a  wing,"  and  thus  means  "  married  wings." 
The  hymenoptera  are  so  called  because  the  upper  and 
under  wings  on  each  side  of  the  body  are  "  wedded  "  or 
linked  together  when  the  insect  is  flying  by  a  row  of  hooks 
and  a  ledge,  a  device  which  is  more  fully  explained  in 
the  next  paragraph.  Like  the  legs,  the  wings  are 
joined  to  the  thorax;  they  are  composed  of  fine  mem- 
branes and  are  strengthened  by  a  kind  of  framework. 
The  ribs  of  this  are  called  the  nervures  (a,  Plate  XXVII.) 
and  are  hollow ;  like  our  veins  they  contain  blood. 

Along  the  top  edge  of  the  lower  whig  is  a  row  of  tiny 
hooks,  while  the  lower  edge  of  the  upper  whig  is  curled 
over,  forming  a  kind  of  ridge  (a,  Plate  XXVIII. ).  There 
is  thus  formed  a  "  hook  and  eye  "  by  which  the  two  wings 
are  locked  together  for  flight  (6,  Plate  XXVIII.) .  By 
these  means  a  large  parr  of  wings  is  formed  which  are 
more  powerful  for  flying  than  would  be  the  case  if  the 
bee  had  only  two  small  pairs  of  wings  with  no  inter- 
locking device.  The  bluebottle  fly  has  only  one  pair 
of  large  wings,  but  this  arrangement  would  not  be  prac- 
ticable in  the  case  of  the  bee.  If  its  wings  were  not 
divided  the  worker  bee  would  be  unable  to  crawl  into 
the  nursery  cells  to  clean  them  out.  These  cells  measure 
£  inch  in  diameter.  When  the  wings  are  folded  over  the 
bee's  back  they  take  up  only  £  inch.  There  is  thus  just 
sufficient  space  for  the  bee  to  enter  the  cell.  The  blue- 
bottle does  not  need  to  fold  its  wings  closely  over  its 
back,  for  it  has  no  cells  to  clean. 

The  action  of  the  hook  and  eye  is  almost  automatic, 


126  THE  MICROSCOPE. 

for  when  the  bee  takes  to  flight  the  front  wing  is  stretched 
out  from  over  its  back,  and  in  this  operation  it  passes  over 
the  upper  surface  of  the  back  wing.  On  the  ridge  reach- 
ing the  hooks  it  catches  upon  them  and  is  held  fast. 
When  the  bee  comes  to  rest  the  process  is  reversed, 
for  as  the  wings  are  folded  the  ridge  slips  away  from  the 
hooks  that  hold  it. 

The  number  of  hooks  varies,  and  sometimes  more  are 
found  on  one  side  of  the  body  than  the  other.  As  a 
general  rule  the  worker  bee  has  from  eighteen  to  twenty- 
three.  The  queen,  who  seldom  flies,  has  not  so  many — 
sometimes  as  few  as  thirteen.  The  drone  has  large  and 
powerful  wings,  and  the  number  of  his  hooks  varies 
between  twenty-one  and  twenty-six. 

VIII. 

The  abdomen,  containing  the  stomach  and  intestines, 
is  joined  to  the  thorax  by  a  thin  waist.  The  abdomen 
of  the  queen  and  of  the  worker  is  divided  into  six  rings 
or  segments,  but  the  drone,  having  a  somewhat  larger 
body,  has  seven.  Each  segment  itself  is  divided  into 
two  parts,  known  as  the  scelentes,  and  joined  to  one 
another  by  a  delicate  membrane. 

The  bee  has  two  stomachs,  the  honey-sac  and  the 
stomach  proper.  The  honey-sac  is  a  kind  of  store  cham- 
ber in  which  the  nectar  is  kept  after  it  has  been  gathered 
from  the  flower,  until  the  bees  return  to  the  hive.  Lead- 
ing from  it  to  the  stomach  is  a  very  fine  tube  or  duct, 
at  the  end  of  which  is  a  kind  of  stopper  or  valve,  called 
the  "  stomach  mouth/'  By  opening  or  closing  this  the 
supply  of  food  to  the  stomach  may  be  regulated.  The 


THE  BEE'S  STOMACH.  127 

honey-sac  is  relatively  minute,  and  even  when  quite  full 
contains  only  about  one-third  of  an  ordinary  sized  drop 
of  honey. 

The  tube  which  leads  from  it  to  the  stomach  is  lined 
with  minute  hairs,  very  fine  and  pointing  in  a  direction 
away  from  the  honey-sac.  When  nectar  is  taken  in  from 
a  flower,  pollen  grains  may  be  unavoidably  taken  in  also. 
This  is  undesirable,  and  so  the  nectar  is  passed  from  the 
honey-sac  to  the  stomach  by  means  of  the  tube.  The 
nectar  is  then  made  to  return  to  the  honey-sac,  and  in 
this  operation  the  hairs  in  the  tube  act  as  a  strainer  and 
prevent  the  pollen  grains  returning  with  the  nectar. 
This  operation  is  carried  on  while  the  bee  is  flying  from 
flower  to  flower  or  on  the  way  back  to  the  hive. 

Bees  do  not  actually  collect  what  is  called  honey,  but 
they  gather  what  the  flowers  secrete.  This  is  nectar, 
which  may  be  described  as  a  thin  watery  liquid,  contain- 
ing among  other  things  a  large  proportion  of  cane  sugar. 
The  honey-sac  is  filled  with  nectar  gathered  from  flower 
after  flower,  and  while  the  bee  flies  a  change  takes  place 
in  the  nectar,  and  it  becomes  converted  into  honey. 
Some  juices  secreted  by  glands  in  the  abdomen  are  added 
to  it  and  the  cane  sugar  is  changed  into  another  form, 
called  grape  sugar. 

IX. 

Insects  breathe  through  tiny  air-holes  called  "spiracles," 
from  the  Latin  spirare,  "  to  breathe  "  (Plate  XXX.). 
Crawling  insects  do  not  require  so  much  air  as  flying 
insects,  and  their  breathing  apparatus  is  therefore  not  so 
large.  In  a  bee  the  breathing  tubes  spread  over  almost 


128  THE  MICROSCOPE. 

the  whole  body,  two  of  the  largest  extending  along  each 
side  of  the  abdomen.  These  air  tubes  branch  off  one 
from  another  like  the  roots  of  a  tree.  The  majority  are 
exceedingly  minute,  a  bundle  of  a  quarter  of  a  million 
being  required,  it  is  estimated,  to  equal  in  size  a  human 
hair.  The  rings  of  the  abdomen  slightly  overlap  one 
another,  and  as  the  bee  draws  in  and  then  drives  out  the 
air,  in  the  act  of  breathing,  these  rings  constantly  slip 
in  and  out.  The  spiracles  are  protected  by  a  number  of 
tiny  hairs  which  keep  out  dust  and  other  foreign  bodies 
which  would  interfere  with  the  breathing. 

X. 

The  sting  is  situated  at  the  tip  of  the  abdomen  and  con- 
sists of  several  parts.  The  sting  itself  is  very  smooth 
and  hard,  and  terminates  in  a  delicate,  lance-like  point, 
compared  with  which  an  ordinary  fine  sewing  needle 
looks  like  a  bar  of  iron  (c,  Plate  XXVII.).  This  sting 
is  really  a  sheath,  in  which  are  enclosed  two  needle-like 
darts.  On  the  outside  of  the  sheath  at  the  end  are  two 
rows  of  three,  or  sometimes  more,  barbs  pointing  back- 
wards. These  prevent  the  sheath  slipping  out  of  the 
flesh  into  which  it  has  been  forced,  until  the  operation 
of  stinging  is  completed.  The  darts  in  the  sheath  can 
be  moved  up  and  down  by  a  powerful  set  of  muscles  at 
the  root  of  the  sting.  They  act  like  drills,  and  come  into 
play  as  soon  as  the  sheath  has  made  an  opening  for  them. 
They  move  up  and  down  at  a  great  speed,  piercing  deeper 
and  deeper  into  the  flesh  of  the  victim  each  time.  They, 
too,  have  barbs  (b,  Plate  XXVII.),  and  near  each  barb 
is  a  minute  hole  leading  to  a  central  hollow  in  the  dart. 


PLATE    XX  XT 


Fr>m  a  water-colour  drawing  by] 


[G.  1-ishcr-Jones 


(«)  Part  of  a  Butterfly's  wing.       (£)  Scales  from  the  Diamond  Beetle. 
(c)   Feather  from  Humming  Bird. 


THE  BEE'S  STING.  129 

Down  this  hollow  and  through  the  holes  in  the  dart- 
barbs  a  poisonous  fluid  is  poured  which  causes  the  pain 
of  a  sting.  The  poison  is  composed  largely  of  formic 
acid,  and  is  secreted  in  a  poison-bag  near  the  root  of  the 
sting  (a,  Plate  XXIX.).  It  is  forced  down  the  central 
hollow  of  the  darts  by  two  muscles  acting  as  pumps. 
The  sting  of  a  worker  bee  is  quite  straight,  but  that  of 
the  queen  is  curved  .like  a  scimitar.  The  drone  has 
no  sting. 


(2,084)  17 


CHAPTER  XII. 

OTHER   INSECTS. 

I. 

AS  in  the  case  of  plants,  insects  are  full  of  interest 
JLjL  to  the  microscopist ;  even  the  most  common  will 
reveal  points  of  interest  when  seen  under  the  microscope, 
and  they  will  furnish  unlimited  material  for  months  of 
study  during  the  long  nights  of  winter.  Specimens 
should  be  collected  during  the  summer,  and  may  be 
preserved  in  weak  acetic  acid  for  a  very  long  time,  for 
examination  at  leisure.  They  may  then  be  studied  just 
as  they  are,  or  if  desired  may  be  dissected,  their  internal 
organs  examined,  and  further  interest  added  by  mounting 
all  the  parts  on  a  card,  neatly  numbering  and  naming 
them.  Butterflies,  spiders,  flies,  beetles,  wasps,  fleas, 
ants,  and  the  like,  all  are  worthy  of  attention. 

There  is  so  much  of  interest  that  it  is,  of  course,  quite 
impossible  to  describe  fully  even  a  fraction  of  the  objects. 
I  can  only  mention  a  few,  and  those  very  briefly,  so  that 
you  may  have  an  idea  of  what  a  wonderful  storehouse  of 
interest  awaits  you. 

Insects  are  sometimes  divided  into  two  groups,  which 


INSECT  "FRIENDS"  AND  "ENEMIES."         131 

are  called  "  friends  "  and  "  enemies."  This  distinction 
is  not,  of  course,  a  scientific  one,  but  it  may  serve  as 
a  guide  and  be  of  assistance  to  the  memory  to  know 
whether  a  certain  insect  is  helpful  or  not  to  us.  It  is 
very  necessary  that  we  should  learn  all  we  can  about  the 
habits  and  life-history  of  the  insects  we  are  studying 
before  classifying  them  as  friends  or  enemies,  because 
otherwise  we  might  easily  make  a  mistake.  For  instance, 
a  person  who  has  just  been  stung  by  a  bee  will  probably 
be  quite  convinced  that  bees  should  be  included  among 
the  "  enemy  "  insects.  On  the  other  hand,  the  bee-keeper 
will  show  his  hives  and  dozens  of  beautifully  sealed 
sections  of  honey  he  has  obtained  from  each  hive.  He 
will  tell  you  that  to  say  bees  should  be  classed  as  enemy 
insects,  just  because  they  can  sting  and  hurt,  is  ridiculous. 

Among  useful  insects  may  be  classed  those  which  fer- 
tilize flowers  and  those  which  give  us  honey,  silk,  dyes, 
and  medicines.  In  the  other  group  fall  the  insects  which 
destroy  clothing,  food,  and  similar  materials,  and  also 
those  which  spread  disease.  The  study  of  insects,  or 
entomology  as  it  is  called,  is  indeed  a  fascinating  one, 
and  one  which  presents  a  very  wide  field,  for  in  Great 
Britain  alone  there  are  tens  of  thousands  of  varieties  of 
insects.  It  is  a  study  in  which  there  are  endless  problems, 
for  sometimes  the  habits  of  association  of  the  little  crea' 
tures  and  the  exhibitions  of  their  wonderful  instinct 
seem  almost  human. 

Insects  may  be  classified  according  to  the  manner  in 
which  they  feed — either  by  biting  or  sucking — or  by  the 
presence  or  absence  of  wings.  In  the  latter  method  the 
following  groups  are  commonly  recognized  : — 


132 


THE  MICROSCOPE. 


Classification. 

Characteristic. 

Example. 

Aphaniptem 
Coleoptera 
Lepidoptera 
Diptera 
Orthoptera 
Neuroptera 
Hymenoptero, 
Thysanoptera 
Homoptera 
Hekeroptera 

wingless 
sheath-winged 
scale-winged 
two-winged 
straight-winged 
nerve-  winged 
membrane-  winged 
tassel-winged 
similar-winged 
dissimilar-  winged 

Fleas 
Beetles 
Butterflies 
Flies 
Grasshoppers 
Dragon-flies 
Bees 
Thrips 
Aphides 
Bugs 

II. 

The  Drone  Fly  (Eristalis  tenax)  very  closely  resembles 
a  bee,  and  may  easily  be  mistaken  for  one  when  on  the 
wing.  It  has  a  wonderful  foot  like  a  double  claw,  and 
with  this  contrivance  it  is  able  to  grasp  very  firmly  any 
object  to  which  it  wishes  to  cling.  This  is  the  reason  it  is 
called  tenax,  because  this  word  is  derived  from  the  Latin 
meaning  "  to  hold."  Its  larvae  inhabit  filth  and  mud, 
devouring  garbage  and  acting  as  scavengers.  In  these 
surroundings  breathing  is  often  difficult,  so  Nature  has 
fitted  the  larvae  with  long,  telescopic  tails,  through  which 
they  can  breathe. 

The  tongue  of  the  drone  fly  is  split  up  a  little  way,  and 
then  again  joined,  and  the  mouth  parts  are  converted  into 
lancet-shaped  organs.  Not  only  are  these  darts,  with 
which  the  skin  of  animals  is  pierced,  but  they  also  act 
as  tubes  through  which  their  blood  may  be  sucked  up. 
Another  part  of  this  insect's  mouth  resembles  in  appear- 
ance a  two-edged  sword,  while  yet  another  has  pincer-like 
cutting  teeth  at  its  extremity.  It  is  a  peculiar  tool  and 


PLATE  XXXII 


THE  ICHNEUMON  FLY.  133 

resembles  an  instrument  used  by  a  surgeon  to  enlarge 
a  wound.  It  is  actually  used  for  this  same  purpose  by 
the  fly,  so  that  the  flow  of  blood  may  be  increased. 

III. 

The  Ichneumon  fly  helps  to  keep  down  caterpillars.  The 
caterpillar  pest  of  1917  and  1918  was  attributed  by  some 
naturalists  partly  to  the  fact  that  one  cause  and  another 
had  killed  off.  the  Ichneumon  flies.  The  caterpillars  had 
thus  obtained  the  upper  hand,  as  it  were,  and  multiplied 
so  profusely  as  to  become  a  serious  menace  to  fruit- 
growers and  farmers.  The  Ichneumon  is  equipped  with 
a  sharp  ovipositor,  or  egg-laying  appendage.  With  this 
it  pierces  the  skin  of  the  caterpillar  and  deposits  its 
minute  eggs  in  the  caterpillar's  body.  It  is  believed  that 
the  caterpillar  does  not  feel  the  operation,  for  it  will  even 
go  on  eating  while  it  is  being  performed.  Later  the  eggs 
hatch  out  into  tiny  grubs  which  feed  on  the  fatty  sub- 
stances in  the  caterpillar's  body.  When  the  caterpillar 
has  finished  eating  and  is  ready  to  turn  into  a  chrysalis, 
the  young  Ichneumon  grubs  leave  it  and  spin  them- 
selves bright  yellow  cocoons.  The  caterpillar  not  having 
any  store  of  fat  to  draw  upon  during  its  chrysalis  state, 
shrivels  up  and  dies  from  lack  of  nutriment. 

IV. 

Like  bees,  ants  may  be  either  social  or  solitary  insects. 
That  is  to  say,  some  species  live  in  colonies,  as  do  bees 
in  a  hive,  while  others  live  by  themselves,  like  the  mason 
bee,  building  their  own  little  nests  and  leading  a  solitary 
life.  Those  ants  which  live  in  colonies  again  resemble 


134  THE  MICROSCOPE. 

bees,  there  being  a  queen,  males,  and  workers.  The 
commoner  kind  are  the  Formicida,  the  queen  and  males 
of  which  sometimes  have  wings.  This  causes  them  to  be 
mistaken  by  some  people  for  flies.  Under  the  microscope 
the  ant  is  seen  to  have  two  large  compound  eyes,  and 
three  simple  eyes  in  front,  like  the  bee.  Some  workers 
are  without  eyes.  The  antenna  are  many  jointed,  and 
the  jaws  sometimes  larger  than  the  head  itself.  Some 
ants  have  minute  sets  of  teeth,  arranged  like  the  edge 
of  a  saw. 

V. 

The  aphis,  more  commonly  known  as  the  "  green-fly," 
which  often  infests  rose-trees,  is  a  curious  insect,  as  seen 
under  the  microscope.  It  is  sometimes  called  the  plant 
lice  and  has  a  beak-like  mouth.  With  this  it  pierces  the 
tender  shoots  of  a  plant  and  sucks  up  the  sap,  thus 
causing  the  plant  to  be  damaged  and  sometimes  killed. 
The  sap  is  partly  given  out  again  by  the  insect  through 
two  protuberances  on  its  hinder  part.  Ants  know  of 
this  fact  and  they  domesticate  aphides,  keeping  them 
as  we  do  cows,  for  the  sake  of  the  sweet  fluid  they  exude. 
This  fluid,  called  honey-dew,  is  obtained  from  the  aphides 
by  "  milking,"  a  process  in  their  case  which  consists  of 
the  ants  stroking  them  tenderly  with  their  antenna. 

Aphides  are  reproduced  at  an  alarming  rate.  It  has 
been  calculated  that  the  descendants  or  progeny  of  a 
single  aphis  in  one  summer  will  number  a  quint illion. 
At  this  rate  the  Earth  would  very  soon  become  a  mass  of 
aphides,  if  it  were  not  for  the  fact  that  they  are  food  for 
many  other  insects.  The  larvae  of  the  "  lady-bird  " 


A  BUTTERFLY'S  WING.  135 

eat  great  quantities  of  aphides,  for  instance,  and  this  helps 
to  keep  the  pest  in  check. 

VI. 

Butterflies  and  moths  are  very  beautiful  objects  in 
the  microscope,  and  among  them  may  be  found  some  of 
the  most  lovely  sights  revealed  to  us.  The  colours  of 
their  wings,  beautiful  as  they  are  to  the  naked  eye,  are 
enhanced  a  hundred-fold  even  with  a  low  power,  and  no 
pen  can  adequately  describe  their  beauty.  The  wings 
are  composed  of  membranes,  covered  with  thousands 
of  tiny  scales,  and  thus  it  is  that  these  insects  belong  to 
the  order  of  Lepidoptem,  for  the  word  lepis  means  "  a 
scale/'  These  minute  scales  form  the  dust  which  is  left 
on  our  fingers  should  we  take  hold  of  a  butterfly's  wing. 
If  a  little  of  this  dust  be  shaken  on  to  a  slip  of  glass  and 
placed  under  the  microscope  the  scales  will  be  clearly  seen. 
Each  scale  is  held  to  the  wing  by  a  tiny  root.  The  scales 
lie  upon  the  wing  membrane  in  rows,  overlapping  each 
other  like  the  slates  on  the  roof  of  a  house,  and  they  pro 
tect  the  delicate  membrane  against  dew  and  rain. 

In  a,  Plate  XXXI.,  is  shown  a  portion  about  TV  inch 
diameter  of  a  tiny  white  dot  in  the  "  eye-spot "  of  the 
fore-wing  of  a  Peacock  butterfly  (Vanessa  io).  The 
scales  of  butterflies  are  actually  coloured,  and  therefore 
differ  from  the  scales  of  some  insects,  which  are  iridescent, 
or  rainbow-hued.  To  this  latter  class  belong  the  scales 
of  the  small  Diamond  Beetle  (Curculis  imperialis)  shown 
at  b,  Plate  XXXI.,  which  owe  their  colour  to  their  ex- 
treme thinness  and  their  transparency,  as  in  the  case  of 
the  soap-bubble  or  oil  on  water.  There  is  still  another 


136  THE  MICROSCOPE. 

class  of  scales  which  glow  with  colour  caused  by  the 
breaking-up  of  white  light  by  numerous  extremely  narrow 
lines  or  furrows  with  which  their  surface  is  covered.  A 
very  good  example  of  this  type  is  afforded  by  the  minute 
brilliant  feathers  in  the  breast  of  a  Humming  Bird  (c, 
Plate  XXXI.).  Those  of  you  who  are  interested  in  the 
explanation  of  this  beautiful  iridescent  colouring  may 
pursue  the  matter  farther  by  studying  some  book  on 
Light,  which  deals  with  the  interference  of  light  caused 
by  thin  films  and  with  diffraction  caused  by  fine  surface 
rulings  or  striated  sui  faces. 

VII. 

The  proboscis  or  tongue  of  the  butterfly  often  reaches 
an  enormous  length  in  some  species.  By  its  aid  the  insect 
is  able  to  reach  deep  down  into  the  corollas  of  flowers 
to  extract  the  nectar  secreted  there.  When  not  in  use 
the  tongue  is  curled  up  like  the  hair-spring  of  a  watch. 

We  have  already  seen  how  flowers  are  fertilized  by 
insects,  and  how  important  it  is  that  the  pollen  should  be 
carried  to  the  stigma.  Much  of  this  work  of  fertilization 
is  done  by  bees,  but  there  are  some  flowers  which  bees 
cannot  fertilize,  owing  to  the  shape  of  their  corollas. 
Honeysuckle  and  convolvulus,  for  instance,  have"  corollas 
so  long  that  the  bee's  tongue  cannot  possibly  reach  the 
nectar  stored  at  the  base.  Flowers  such  as  these  depend 
on  butterflies  and  moths  for  their  fertilization,  so  we  find 
that  these  insects  are  provided  with  exceptionally  long 
tongues.  As  moths  fly  by  night,  it  is  then  that  the 
flowers  which  wish  to  attract  them  put  out  their  choicest 
perfumes,  for  the  sweet  smell  guides  the  moths  to  them. 


PLATE  XXXIII 


From  a  photo-micrograph  by] 

THE    TONGUE   OF   A   BLOW-PLY 


[A.  E.  Smith 


THE  SILKWORM.  137 

VIII. 

Among  the  useful  insects  must  be  included  the  silk- 
worm (Bombyx  mori).  No  doubt  many  of  you  have  kept 
silkworms,  and  studied  their  interesting  habits.  You 
will  therefore  know  that  this  insect  is  not  a  "  worm  " 
at  all,  but  a  moth,  which,  like  all  moths  and  butterflies, 
is  first  a  caterpillar,  hatched  from  a  tiny  egg.  It  feeds 
on  leaves  and  sheds  its  skin  from  time  to  time  as  it  grows, 
an  operation  which  is  made  easier  by  the  secretion  of  an 
oily  fluid  between  the  new  and  the  old  skins.  When  fully 
grown  the  caterpillar  commences  to  spin  a  cocoon  of 
silk.  The  thread  issues  from  a  spinneret  and  is  something 
similar  to  the  thread  of  a  spider's  web.  In  the  silkworm, 
however,  the  spinneret  is  not  situated  in  the  abdomen, 
but  in  a  nipple-like  swelling  on  the  caterpillar's  lower 
lip.  As  the  fine  thread  issues  from  this  spinneret  it 
hardens  on  exposure  to  the  air.  The  spinning  of  the 
cocoon  takes  about  four  or  five  days,  and  the  amount 
of  thread  spun  is  about  1,000  feet  in  length.  When  the 
silkworm  is  kept  for  profit,  this  thread  is  subsequently 
unwound  by  mechanical  means,  and  is  then  spun  into 
silk  proper.  It  is  estimated  that  this  little  insect  furnishes 
employment  to  over  100,000  people  in  Great  Britain  and 
America  alone,  while  many  fortunes  have  been  made — 
and  lost — through  it. 

IX. 

The  eggs  of  butterflies,  moths,  and  other  insects  furnish 
a  countless  variety  of  objects  for  examination.  To  the 
naked  eye  they  sometimes  appear  as  greyish  spots  on 

(2,084)  1  j 


138  THE  MICROSCOPE. 

the  leaves  of  plants,  often  occurring  in  clusters.  In  the 
microscope  we  find  them  to  have  a  beautiful  pearly-white 
appearance,  often  delicately  coloured,  with  yellow,  green, 
or  red.  They  are  of  all  manner  of  shapes  and  designs 
(b,  Plate  XXXII.) .  Some  are  perfectly  smooth,  others 
are  fluted  and  ribbed,  sculptured  with  rims  and  grooves 
which  run  over  their  entire  surface.  So  distinct  are  these 
varieties  that  a  microscopist  should  easily  be  able  to  name 
the  butterfly  by  seeing  its  egg.  Some  butterflies  have 
such  beautiful  eggs  that  they  are  even  of  more  beautiful 
design  than  the  eggs  of  birds. 

Butterflies'  eggs  are  not  surrounded  by  a  shell  of  car- 
bonate of  lime,  as  are  those  of  birds,  but  consist  of  a 
tough,  gelatinous  substance  which  resists  strong  acids. 
This  so  effectively  protects  the  tiny  germs  within  against 
the  elements,  that  the  eggs  even  may  be  frozen  in  a  block 
of  ice  without  killing  them.  They  are  thus  able  to  with- 
stand a  severe  winter  and  carry  over  butterfly  life  to  the 
following  spring,  the  warm  days  of  which  hatch  out  the 
tiny  caterpillars. 

Butterflies'  eggs,  as  well  as  those  of  moths,  are  very 
minute  objects.  They  vary  in  size  from  less  than  -^  inch 
to  TV  inch  in  diameter.  The  former  would  easily  drop 
through  a  hole  made  in  a  piece  of  paper  by  a  pin.  They 
are  generally  of  two  kinds,  "  upright  "  and  "  flat,"  and 
may  be  laid  in  large  batches  or  singly.  They  are  found  in 
all  kinds  of  places — on  bark  or  twigs  of  trees  in  the  winter, 
and  in  grass  or  on  leaves  in  the  summer.  As  a  rule  the 
mother  butterfly  takes  care  to  lay  the  eggs  on  the  leaves 
of  the  tree  on  which  the  young  caterpillar  likes  best  to 
feed,  so  that  when  it  hatches  out  it  will  have  plenty  of 


BUTTERFLIES'  EGGS.  139 

food  ready  to  hand.  Sometimes  the  tiny  caterpillar  may 
be  seen  inside  the  egg,  which  always  changes  colour 
and  appearance  as  the  time  for  hatching  approaches. 
A  caterpillar  may  take  from  five  or  six  days  to  nine 
months  to  hatch  out  from  the  egg,  according  to  the 
particular  variety  of  butterfly  or  moth  to  which  the 
insect  belongs.  Some  pass  the  winter  in  the  egg,  but 
others  hatch  out  in  a  few  days,  and  in  the  course  of  time 
become  butterflies,  the  whole  operation  taking  place 
during  the  same  summer  in  which  their  mother  lived. 


W 

FIG.  42. — Eggs  of  (a)  Large  White  Butterfly.    (6)  Elephant  Hawk  Moth. 
(c)  Scalloped  Oak  Moth. 

The  eggs  of  the  Large  White  Butterfly  (Pieris  bras- 
sicce]  are  as  remarkable  as  any.  They  are  golden  yellow, 
upright,  and  have  well-defined  ribs  which  run  longi- 
tudinally (a,  Fig.  42).  They  may  be  found  in  clusters 
during  June,  generally  in  the  leaves  of  cabbages,  and 
other  similar  plants,  upon  which  the  caterpillar  feeds. 
The  eggs  of  the  Painted  Lady  (Pyrameis  cardui)  are  also 
upright  and  of  a  pale  green  colour.  They  also  have 
longitudinal  ribs,  and  are  formed  in  June,  singly,  on 
thistles  and  nettles.  The  eggs  of  the  Elephant  Hawk 
Moth  (Chcerocampa  elpenor)  are  flat  and  oval-shaped 


I4o  THE  MICROSCOPE. 

(b,  Fig.  42).  They  are  green  in  colour,  smooth,  and  are 
not  decorated  at  all.  They  are  laid  in  July  on  bedstraw, 
willow-herb,  and  similar  plants,  usually  those  near  some 
stream  or  pond. 

The  Scalloped  Oak  Moth  (Crocallis  elinguaria)  lays 
flat  eggs  which  are  oblong  and  smooth  (c,  Fig.  42). 
They  are  brownish  white  in  colour,  with  patches  of  dark- 
brown,  and  are  usually  found  in  straight  rows,  side  by 
side,  along  blackthorn  twigs.  They  are  laid  in  July  and 
August,  and  will  not  hatch  until  the  following  spring. 

X. 

At  one  time  the  house-fly  was  looked  upon  by  some 
people  as  being  one  of  our  insect  friends,  for  it  acts  as  a 
scavenger,  eating  up  refuse.  Further  investigations  more 
recently  have  shown  that  flies  are  very  harmful  to  us, 
for  they  carry  disease,  and  it  is  because  of  this  that  we 
have  been  requested  by  posters  and  public  notices  to 
"  kiU  that  fly." 

The  common  house-fly  (Musca  domestica)  has  one  pair 
of  wings,  and  is  therefore  classed  among  the  diptera  or 
double-winged  insects.  Its  wings  consist  of  a  double 
membrane,  strengthened  by  nervures  like  those  of  the 
bee.  It  has  also  two  appendages,  the  halteres  or  poisers, 
and  these  are  sometimes  called  undeveloped  or  rudi- 
mentary wings.  They  seem  to  act  as  balances  and  enable 
the  fly  to  walk  in  difficult  circumstances. 

The  house-fly's  tongue  is  a  common  object  in  the 
microscope,  and  the  proboscis  of  the  blow-fly  is  a  well- 
known  object  for  testing  the  quality  and  defining  the 
power  of  lenses  (Plate  XXXIII.).  The  house-fly's  tongue 


PLATE  XXXIV 


From  a  photo-micrograph  by] 


A   GNAT 


[A.  E.  Smith 


THE  HOUSE-FLY.  141 

consists  of  two  parts,  the  pharynx  and  the  mouth  itself. 
The  pharynx  is  a  kind  of  throat  tube  which  extends 
beyond  the  mouth  when  the  fly  is  feeding,  but  when  not 
in  use  it  lies  in  the  head.  The  mouth  itself  is  situated  at 
the  end  of  the  pharynx.  The  proboscis  carries  numerous 
hairs  of  various  shapes — well  seen  in  that  of  the  blow-fly — 
some  of  which  are  thicker  than  others.  Those  at  the  end 
are  tubular,  and  when  the  tongue  is  extended  in  eating, 
these  hairs  fill  with  air  and  stiffen,  thus  protecting  the 
delicate  parts.  When  the  insect  has  finished  eating  and 
draws  in  its  tongue,  the  hairs  are  emptied  of  air,  and 
become  easily  movable,  so  as  not  to  interfere  with  the 
folding  of  the  proboscis  in  the  head. 

The  fly  eats  in  a  curious  manner.  Watch  a  fly  after  it 
has  "  settled  "  on  some  sugar.  It  first  impels  its  pro- 
boscis, and  extending  it  out  of  its  head,  causes  the  two 
broad  fan-like  appendages  to  appear  from  the  top. 
These  act  as  files  and  suckers,  and  with  them  a  little 
sugar  is  filed  off.  The  fly  then  pours  some  fluid  upon 
this  from  its  mouth  organs.  This  forms  a  kind  of  syrup, 
which  is  at  once  sucked  up.  The  tubes  of  the  proboscis 
are  kept  open  by  a  spiral  arrangement  of  hair-like  fibre, 
in  a  similar  manner  that  the  garden  hose-pipe  is  kept 
from  bending,  or  "  kinking,"  by  an  internal  spiral  wire. 
A  fly  does  not  bite  or  sting,  as  we  sometimes  suppose, 
but  grates  or  files  with  the  little  tools  at  the  end  of  its 
proboscis. 

The  fly  has  three  pairs  of  legs,  and  each  is  divided  into 
five  parts.  The  tarsus,  or  foot,  is  fitted  with  two  formid- 
able claws,  also  a  delicate  pad,  carrying  many  tubular 
hairs,  and  covered  with  a  sticky  fluid.  This  enables 


142  THE  MICROSCOPE. 

the  foot  to  adhere  to  slippery  objects,  and  the  fly  is 
thus  able  to  walk  up  a  pane  of  glass  or  similar  smooth 
surface. 

The  fly  has  a  comparatively  large  "  heart,"  or  dorsal 
vessel,  as  it  is  called,  which  beats.  The  blood  flows 
through  the  fly's  body  in  the  reverse  way  to  that  of  ours, 
being  forced  by  the  contraction  of  the  heart  from  tail 
to  head. 

When  we  speak  of  insects  having  blood,  we  do  not 
mean  blood  similar  to  that  of  human  beings  any  more 
than  we  mean  their  dorsal  vessel  is  a  true  heart.  The 
blood  of  insects  is  transparent,  nearly  colourless,  and 
differs  in  other  respects  from  our  blood.  It  is  kept  pure 
by  aeration  by  trachea,  which,  as  we  have  already  seen, 
are  air-tubes  running  through  the  insect's  body. 

Flies  are  to  a  certain  extent  of  use  in  the  economy  of 
nature,  for  they  consume  decaying  matter  that  would  not 
otherwise  be  removed,  and  which  in  hot  weather  would 
perhaps  harbour  disease.  Linnaeus,  a  celebrated  natural- 
ist, said  that  three  flies  would  consume  a  dead  horse  as 
quickly  as  a  lion.  He  meant,  of  course,  these  flies  and 
their  offspring.  It  has  since  been  said  that  the  saying 
is  probably  quite  correct,  since  the  young  begin  to  eat 
as  soon  as  they  are  hatched,  and  a  female  blow-fly  will 
produce  20,000  living  larvae.  In  twenty-four  hours  each 
will  have  increased  in  weight  200  times,  in  five  days 
attaining  their  full  size,  changing  to  the  pupae,  and 
then  to  the  perfect  insect. 

Although  flies  are,  beyond  doubt,  of  some  value  as 
scavengers,  they  are  the  cause  of  much  trouble  in  other 
ways.  The  house-fly  may  carry  germs  of  disease  upon 


PLATE  XXXV 


From  a  photo-micrograph  by] 


A   FLEA 


[A.  E.  Smith 


THE  GNAT.  143 

its  feet  and  proboscis  and,  by  its  dirty  method  of  eat- 
ing— already  described — transfer  these  to  human  food. 
The  larvae  of  the  Bott  fly,  or  "horse-fly,"  often  bore 
into  the  skin  of  sheep  and  cause  these  animals  great 
irritation  and  pain,  which  sometimes  results  in  death. 
The  Tse-tse  fly  is  the  carrier  of  the  organisms  which 
cause  the  dreaded  sleeping  sickness  in  Africa  and  the 
tropics. 

XL 

The  ghat  (Plate  XXXIV.)  has  very  graceful  antenna, 
and  indeed,  as  we  might  well  expect,  it  shows  very 
delicate  structures  when  magnified.  The  male  gnat  has 
plumed  antenna,  which  are  marked  by  their  lightness 
and  grace.  As  in  the  case  of  the  bee,  the  gnat's  antenna 
consist  of  many  joints,  generally  about  fourteen,  and  from 
each  of  these  spring  hairs.  In  the  case  of  the  male, 
these  hairs  are  very  numerous  and  of  great  length,  thus 
giving  the  plumed  appearance  already  mentioned. 

Gnat-grubs  may  be  obtained  in  the  summer  from  almost 
any  water-tub  or  pond,  for  they  swarm  on  the  surface 
of  the  water.  These  grubs  are  partly  transparent,  and 
through  the  outer  covering  may  be  seen  the  flat,  rounded 
head,  the  great  swollen  thorax,  and  finally  the  long, 
slender,  many-jointed  body.  The  head  shows  a  pair 
of  rod-like  antenna,  two  black  patches  marking  the  place 
of  the  eyes-to-be,  and  the  jaws,  covered  with  rows  of 
strong  hairs  and  ever  working  with  rapid  vibrations. 
The  thorax  is  so  transparent  that — as  in  the  case  of 
Daphnia — we  may  watch  the  gnat's  heart,  or  dorsal 
vessel,  as  we  should  call  it,  beating  and  pulsating  with 


144  THE  MICROSCOPE. 

beautiful  regularity.  Sometimes  we  may  discern  a  dark 
pellet  of  food  descending  through  the  "  throat,"  and  this 
explains  the  constant  vibrations  of  the  jaws,  which  collect 
the  food  from  the  water  in  minute  particles  and  form  it 
into  a  pellet  to  be  passed  into  the  stomach  when  suffici- 
ently large.  All  these  may  be  seen  if  the  grub  is  young 
enough,  for  then  the  tissues  of  the  outer  covering  are 
beautifully  transparent  and  resemble  amber.  As  the 
insect  grows  older,  however,  the  tissues  become  opaque 
and  the  fine  details  cannot  be  made  out. 

To  a  certain  extent  the  wings  of  the  gnat  resemble 
those  of  the  bee.  Two  transparent  membranes  are 
strengthened  by  nervures.  Both  sides  are  covered  with 
numerous  and  minute  short  spine-like  hairs,  while  along 
the  nervures  and  outer  edges  of  the  wings  are  set  long 
hair-like  scales.  When  one  of  these  scales  is  examined 
with  a  high  power  it  is  seen  to  be  a  leaf-shaped  plate  of 
transparent  substance  and  of  curious  appearance. 

XII. 

Another  common  insect — rightly  classed  among  the 
"  enemies  "—is  the  flea  (Plate  XXXV.).  This  was  a 
favourite  object  for  examination  and  show  purposes  with 
early  microscopists.  The  flea  does  not  "  bite/'  although 
its  attentions  are  so-called.  In  its  mouth-part  is  a  fine, 
sharp  piercing  organ  like  a  lancet.  With  this  it  pricks 
the  skin  of  its  victim  and  sucks  out  the  blood.  The 
irritation  is  caused  by  the  flea  injecting  into  the  wound 
a  drop  of  poisonous  liquid,  by  which  the  blood  of  the 
victim  becomes  more  fluid  and  thus  is  more  easily 
sucked  up. 


PLATE  XXXVI 


From  photo-micrographs  by]  (b)  [C.  D.  Holmes 

<&)  SPINNERETS    OP   THE    SPIDER.       (b)  SPIDER'S   CLAW 


MITES  AND  TICKS.  145 

XIII. 

Mites  and  ticks  are  not  insects,  but  are  really  associated 
with  spiders.  As  they  are  "  fleas  "  to  animals  and  in- 
sects, however,  we  may  perhaps  say  a  word  or  two  about 
them  here.  In  the  perfect  state  they  resemble  spiders 
in  the  number  of  their  legs,  eight.  Sometimes  they  are 
found  with  only  six  legs,  sometimes  with  even  only  four, 
but  when  found  thus  they  are  in  an  immature  state. 
Some  find  their  food  in  plants  or  decaying  matter,  but 
others  are  parasites. 

The  Gramasida,  or  insect-mites,  are  perhaps  the  best 
known.  They  may  be  found  on  beetles,  flies,  bees,  and 
other  insects.  They  cling  to  the  bodies  of  their  hosts, 
and  a  hand  lens  will  often  show  their  struggles  in  the 
downy  hairs  which  cover  the  bee's  body. 

Mites  are  also  found  in  fresh  and  salt  water,  in  the 
latter  case  on  seaweed  in  rock  pools.  Fresh-water  mites 
are  often  partly  coloured  with  red  or  purple  and  have 
an  appearance  like  velvet.  At  the  tip  of  their  feelers, 
or  palpi,  they  have  a  tiny  hook,  and  with  this  they  hook 
themselves  to  marine  creatures.  Over  twenty  species 
of  fresh-water  mites  have  been  discovered  in  ponds  in 
England  alone.  Mites  may  also  be  obtained  from  hanging 
hams  or  flour  which  has  been  kept  in  a  bin  for  any  length 
of  time.  The  cheese  mite  (Acarus  domesticus)  is  well 
known,  and  examples  may  be  obtained  from  cheese 
which  has  been  kept  a  long  time. 

Ticks  are  somewhat  larger  than  mites,  are  oval  in 
shape,  and  have  a  sucking  mouth.  Some  are  blind,  but 
others  have  eyes.  They  live  on  herbage,  as  a  rule. 

(2,084)  19  * 


146  THE  MICROSCOPE. 

The  female  sometimes  causes  a  great  deal  of  trouble 
by  piercing  the  skin  of  some  warm-blooded  animal 
and  sucking  its  blood.  Much  pain  and  suffering  is 
thus  caused  to  cattle.  Sometimes  when  walking  in  the 
fields  you  may  have  seen  a  starling  pecking  away  in 
a  curious  way  at  the  fleece  of  some  sheep.  These  birds 
are  really  feeding  upon  the  sheep's  ticks  entangled  in 
the  wool.  The  sheep  goes  on  eating  its  grass  while  the 
operation  is  in  progress,  well  pleased  no  doubt  at  the 
efforts  of  these  birds  to  free  it  from  the  painful  pest. 
The  sheep  tick,  however,  is  an  insect,  and  not  really  a 
tick.  It  has  only  six  legs,  and  is  placed  among  the 
lower  flies — diptera — although  it  has  no  wings.  It  is 
thought  that  the  sheep  tick  is  a  descendant  of  some  higher 
type  of  insect,  and  that  probably  it  has  become  a  parasite 
owing  to  its  remote  ancestors  acquiring  the  habit  of 
feeding  themselves  at  the  expense  of  other  animals. 
Becoming  too  lazy  to  seek  its  food  by  hard  work,  it 
obtained  it  easily  and  without  much  effort  in  the  manner 
already  indicated.  Now,  Nature  has  decreed  that 
faculties  which  remain  inactive  and  are  not  wanted 
shall  be  done  away  with.  Thus,  seeing  that  the  sheep 
tick  did  not  use  its  wings,  they  have  gradually  disappeared, 
with  the  result  that  the  sheep  tick  of  to-day  has  none. 
Not  only  is  it  absolutely  dependent  upon  its  host,  there- 
fore, but  also  it  cannot  fly  away  from  the  starling  and 
the  crow,  which  pick  it  out  of  the  sheep's  tangled  wool. 


PLATE  XXXVII 


From  a  photograph  by] 


1 

[W.  Coles-Finch 


YOUNG   SPIDERS   HATCHING   OUT 


CHAPTER  XIII. 
MINIATURE  ENGINEERS:    SPIDERS. 

I. 

THE  spider,  with  its  wonderful  power  of  designing 
and  spinning  webs,  may  indeed  be  called  a  minia- 
ture engineer.  Never  was  a  gulf  bridged  more  effectively 
with  iron  and  steel  than  is  the  space  between  branches 
or  leaves  by  the  web  of  the  spider.  There  is,  however, 
an  important  distinction  between  the  two  bridges,  for 
whereas  that  of  human  beings  is  used  for  traffic,  the  web 
of  the  spider  is  a  trap  or  snare  by  which  the  little  blood- 
sucker obtains  its  food. 

The  name  "  spider  "  is  derived  from  the  old  English 
word  spinder,  "  a  spinner."  You  have  no  doubt  heard 
some  people  speak  of  spiders  as  insects,  but  this  is  not 
scientifically  correct.  They  belong  to  a  sub-class  of 
Anthropoda,  called  Arachnidce,  and  are  related  to  scor- 
pions and  mites.  They  come  between  crustaceans — like 
the  lobsters — and  true  insects  in  their  classification. 
It  is  useful  to  remember  that  the  highest  forms  of  crus- 
taceans have  ten  feet,  Arachnidce  eight,  and  insects  six. 
Also  that  Arachnidce  have  several  simple  eyes,  are  as  a 

147 


148  THE  MICROSCOPE. 

rule  wingless,  have  no  antenna,  and  breathe  by  tracheal 
tubes  and  sacs.  They  are  mostly  carnivorous,  or  flesh- 
eating,  and  because  they  live  on  insects  they  may  be 
regarded  as  friends  by  the  gardener,  for  they  destroy 
many  pests  which  might  otherwise  damage  fruit  and 
flowers.  They  also  help  to  keep  down  what  would 
otherwise  assuredly  be  a  plague  of  flies,  for  the  whole 
tribe  of  spiders  are  fly-butchers  by  profession.  Just  as 
our  butchers  have  their  slaughter-houses,  knives,  pole- 
axes,  and  hooks,  so  these  little  slaughterers  have  their 
nets,  traps,  and  caves,  their  fangs,  hooks,  and  poison 
bags.  "  No  one/'  wrote  Professor  Rymer  Jones,  "  who 
looks  at  the  armament  of  a  spider's  jaws  can  mistake  the 
intention  with  which  this  terrible  apparatus  was  planned. 
'  Murder '  is  engraved  on  every  piece  that  enters  into 
his  composition." 

There  are  about  2,500  known  species  of  spiders,  of 
which  some  550  are  to  be  found  in  the  United  Kingdom. 
Many  of  them  make  most  interesting  pets  and  grow  quite 
tame.  No  doubt  you  have  read  of  the  poor  prisoner 
in  the  Bastille  who  whiled  away  the  long  hours  of  his 
captivity  by  taming  a  spider  which  occupied  his  dungeon 
with  him. 

II. 

The  spider's  body  is  made  up  of  three  parts,  the  head, 
thorax,  and  abdomen,  but  the  head  and  thorax  are  almost 
merged  into  one.  As  in  the  case  of  insects  the  legs  are 
attached  to  the  thorax,  and  are  so  placed  as  to  allow 
great  freedom  of  motion.  The  abdomen  is  of  large  size, 
especially  in  female  spiders,  and  is  often  beautifully 
coloured  and  decorated  with  peculiar  designs.  Especially 


PLATE  XXXVIII 


From  a  photograph  by]  [W.  Coles-Finch 

GARDEN   SPIDER   REPAIRING   WEB 


THE  SPIDER'S  WEB.  149 

is  this  so  in  the  case  of  the  upper  surface,  where  the 
markings  are  like  mosaic,  and  often  take  the  form  of  a 
cross.  The  legs  are  covered  with  stout  bristles  and  are 
provided  with  claws,  of  which  we  shall  speak  later. 

The  majority  of  spiders  have  very  small  mouths,  and 
can  therefore  consume  only  liquid  food,  which  they  suck 
from  their  prey.  In  most  cases  spiders  capture  this  prey 
by  spinning  webs,  and  it  is  because  they  spin  these  webs 
that  the  class  to  which  they  belong  is  called  Arachnidce. 
Arachne  was  a  Lydian  maiden,  so  skilful  in  needlework 
that  she  challenged  Minerva,  the  goddess  of  the  art, 
to  a  trial  of  skill.  Although  Arachne's  hand-work  was 
exquisite,  Minerva's  was  even  more  beautiful.  In  despair 
at  her  work  being  surpassed  Arachne  hanged  herself, 
but  was  changed  into  a  spider  by  the  goddess.  When 
we  see  the  beautiful  work  of  the  spider,  it  is  interesting 
to  recall  this  old  Greek  legend. 

III. 

It  is  the  spinning  of  these  webs  and  the  apparatus  for 
this  work  which  is  the  most  interesting  part  of  the 
spider's  anatomy  to  the  microscopist.  The  spinning 
organs  of  these  spiders  which  construct  circular  webs 
are  the  most  complicated. 

The  gossamer  threads  of  which  the  webs  are  composed 
are  among  the  finest  lines  in  creation.  They  issue  from 
the  spinnerets,  which  are  small  teat-like  swellings  in  the 
under  side  of  the  abdomen  (a,  Plate  XXXVL).  Their 
position  is  well  seen  in  Plate  XXXVIII.,  in  which  is 
depicted  a  female  garden  spider  repairing  her  damaged 
web,  at  the  same  time  holding  a  fly  in  her  mandibles. 


150  THE  MICROSCOPE. 

These  spinnerets  vary  in  number  in  different  spiders,  some 
having  four,  others  six.  Sometimes,  but  not  often,  there 
may  be  as  few  as  two  or  as  many  as  eight.  In  those 
spiders  which  have  six  spinnerets  we  have  to  look  care- 
fully for  the  extra  two,  as  sometimes  it  would  seem  as 
though  there  are  only  four.  The  spider  can  move  the 
spinnerets  as  it  wishes,  raising  or  lowering  them,  and 
using  one,  many,  or  all  of  them,  as  it  requires.  Each 
spinneret  consists  of  a  large  number  of  silk  tubes,  which 
in  the  common  garden  spider  amount  to  600.  There 
are  also  different  kinds  of  spinning  glands,  and  in  this 
same  spider  these  are  five  in  number.  The  silk  of  each 
of  these  glands  differs  in  nature,  and  is  skilfully  employed 
as  required  by  the  spider.  For  instance,  some  of  the 
larger  tubes  in  the  teats  give  out  a  more  sticky  fluid  than 
the  others.  They  are  all  combined  to  form  one  thread, 
as  various  strands  of  hemp  are  combined  to  form  a  rope, 
except  that  the  spider's  strands  are  not  twisted  in  the 
way  that  a  rope  is. 

Nearly  all  spiders  encase  their  eggs  in  a  cocoon  of 
silken  thread,  and  store  them  in  a  sheltered  place.  Here 
they  pass  through  the  cold  days  of  winter  and  await 
the  coming  of  spring  and  warm  weather,  which  will 
hatch  out  the  young  spiders.  In  the  case  of  the  Wolf 
Spider,  the  female  always  carries  the  cocoon  containing 
the  eggs  with  her,  and  vigorously  resists  any  attempt 
to  separate  her  from  it. 

IV. 

The  spider  does  not  undergo  metamorphosis,  or  "  change 
of  form,"  like  many  insects,  such  as  butterflies  and  bees, 


PLATE  XXXIX 


From  a  photograph  by]  [W.  Coles-Finch 

WEB   OF   GARDEN    SPIDER    COVERED   WITH    DEW 


THE  GARDEN  SPIDER.  151 

which  are  first  eggs  and  then  become  grubs,  before  they 
finally  assume  the  perfect  state  of  the  fully  developed 
insect.  Spiders  resemble  the  cockroach  and  grasshopper, 
assuming  the  adult  form  as  soon  as  hatched,  and  thus 
developing  direct  from  an  egg  to  a  spider.  The  female 
spider  lays  her  eggs  in  the  early  autumn,  producing 
perhaps  200  or  300  in  quick  succession.  She  rolls  them 
into  a  kind  of  ball  with  her  legs,  encircles  them  with  a 
thick  covering  of  web,  and  deposits  them  in  some  shel- 
tered position.  You  may  often  find  one  of  these  nests 
in  some  garden  wall  or  fence,  looking  like  a  large  chrysalis 
of  a  pale  yellow  colour.  Sometimes  it  is  covered  with 
dirt  and  leaves  which  match  the  surroundings.  These 
the  spider  has  woven  into  the  outer  layers  for  protection, 
for  the  cocoon  is  a  delicate  morsel  for  hungry  birds  at  a 
time  of  the  year  when  food  is  scarce.  When  the  spring 
comes,  the  eggs  hatch  and  myriads  of  tiny  spiders  are 
to  be  seen — in  some  cases  no  larger  than  a  pin's  head — 
all  busily  occupied  in  exercising  their  legs  as  well  as  their 
silken  surroundings  will  allow  (Plate  XXXVII.).  These 
soon  commence  housekeeping  on  their  own  account,  as 
the  numerous  webs  on  surrounding  plants  and  bushes 
testify. 

V. 

One  of  the  best-known  spiders  is  the  Garden  Spider, 
already  mentioned  (Plate  XXXVIII.) .  Its  scientific 
name  is  Epeira  diademata,  and  it  is  the  largest  variety 
found  in  this  country.  It  may  easily  be  recognized  by 
the  white  and  yellow  spots  with  which  its  body  is  covered, 
and  the  dark  bands  and  spines  on  its  long  legs.  Its  body 


152  THE  MICROSCOPE. 

is  usually  some  shade  of  brown  or  grey,  although  some- 
times it  may  be  vivid  green,  or  even,  chameleon-like, 
change  colour  with  its  surroundings. 

It  has  four  pair  of  eyes  arranged  in  two  rows  ;  the 
male  is  much  smaller  than  the  female  and  is  often  in 
danger  of  his  life,  especially  after  paying  his  attentions 
to  the  female,  for  she  frequently  makes  a  meal  of  him  ! 
If  he  is  wise  the  male  spider  will  leave  a  line  of  web 
hanging  near  by  when  he  goes  a-courting.  He  can  then 
rapidly  escape  from  the  side  of  the  female  if  she  attempts 
to  eat  him,  and  as  the  hanging  line  is  not  strong  enough 
to  bear  the  weight  of  the  female  the  male  will  escape  if 
he  is  quick  enough.  Sometimes  both  male  and  female 
will  li ve  together  in .  quite  a  friendly  manner.  One 
particular  pair  I  know  of  shared  the  same  geranium  leaf 
day  after  day,  huddling  close  together  during  the  nights 
in  the  same  web. 

The  Garden  Spider  spins  the  beautiful  geometrical  web 
which  looks  so  exquisite  in  the  early  morning  when  covered 
with  thousands  of  dewdrops  (Plate  XXXIX.) .  When  spin- 
ning its  web,  the  spider  first  lays  the  foundations,  or  the 


FIG.  43.— Threads  of  spider's  web.     (a)  Trapping  lines. 
(6)  Web  lines. 

"  spokes  "  of  the  wheel-design.  These  consist  of  a  strong 
and  simple  double  thread,  which  hardens  rapidly  by 
exposure  to  the  air  (b,  Fig.  43).  Then,  lying  across  this 
scaffolding,  are  placed  the  circular  threads  like  the  main- 


From  a  photograph  by]  [J.  Holmes 

TRANSPARENT   NEST   OP   WATER    SPIDER 


THE  SPIDER'S  LEGS.  153 

spring  of  a  watch.  These  threads  are  covered  with  a 
sticky  fluid  from  the  larger  tubes,  and  in  the  microscope 
look  like  a  thread  strung  with  minute  beads  (a,  Fig.  43). 
It  has  been  estimated  that  as  many  as  120,000  of  these 
globules  are  contained  in  a  large  web. 

VI. 

Spiders  spin  their  webs  as  traps  in  which  to  catch 
flies  and  other  insects  which  they  require  for  food.  Some- 
times a  web  may  be  completely  spun  in  forty-five  minutes, 
or  it  may  occupy  as  long  as  four  or  five  hours.  When  it 
is  finished,  Epeira  will  wait  in  the  centre  of  the  web, 
or  concealed  close  by  in  a  den  of  leaves.  If  the  latter  is 
the  case  she  will  generally  lay  a  trap  line  from  the  hub, 
or  centre  of  the  web,  to  her  den,  by  means  of  which  she 
can  instantly  tell  when  a  fly  has  touched  the  snare. 
Spiders  are  largely  dependent  upon  their  sense  of  touch 
for  information  as  to  what  takes  place  in  their  web. 

A  spider  has  eight  legs,  each  curiously  constructed 
and  terminating  in  a  strong,  horny  claw,  having  the 
appearance  of  a  small  comb  (b,  Plate  XXXVI.) .  The 
teeth  of  this  comb  are  set  close  together  and  enable  the 
spider  to  obtain  a  firm  foothold  in  its  web,  and  thus  she 
is  able  to  walk  easily  on  a  single  strand.  Her  feet  not 
only  regulate  the  issue  of  the  silken  threads  and  separate 
them,  but  also  they  are  sensitive  to  an  exquisite  degree. 
It  is  by  resting  them  on  the  trap  line,  already  mentioned, 
that  the  spider  is  able  to  feel  when  a  fly  has  entered 
her  web. 

It  is  believed  that  a  spider  resorts  to  a  practice  known 
as  "  trolling  the  fly."  She  attaches  a  strand  to  her 

'2,084)  20 


I54  THE  MICROSCOPE, 

victim,  already  helplessly  entangled  in  the  meshes  of  her 
web,  and  turns  the  fly  round  and  round  like  a  joint  on 
a  spit.  By  these  means  the  fly  is  soon  completely  en- 
tangled in  the  silken  strand  and  is  left  trussed  up,  hanging 
like  a  ham  from  the  ceiling  of  a  farmhouse.  If  a  wasp  or 
heavy  insect  blunders  into  the  web,  the  spider  is  out  at 
once,  drawing  long  threads  around  her  struggling  prey 
from  a  safe  distance.  Once  the  prey  is  bound,  it  is  soon 
inflicted  with  a  bite  from  the  spider's  poison  fangs, 
and  its  doom  is  sealed. 

The  water  spider  (Argyroneta  aquatica)  is  an  extremely 
interesting  pet,  which  can  be  kept  in  an  aquarium. 
It  builds  a  dome-shaped  nest,  something  like  a  thimble, 
below  the  surface  of  the  water  (Plate  XL.).  This  is  a 
curious  habit,  for  the  spider  is  only  fitted  out  for  air- 
breathing.  She  overcomes  the  difficulty,  however,  by 
carrying  down  to  the  nest  each  time  she  dives  a  bubble 
of  air  which  becomes  entangled  in  the  hairs  of  her  body. 
To  see  her  carrying  down  the  silver  bubbles,  and  filling 
her  nest  with  air,  converting  it  into  a  tiny  diving  bell, 
is  indeed  a  fascinating  sight. 

Space  forbids  my  describing  any  more  of  the  wonders 
of  spiderland,  but  if  you  wish  to  do  so,  you  can  learn 
for  yourself  of  the  wonderful  instinct  of  the  mother  spider 
for  her  young,  of  the  industry  of  spiders,  of  the  ballooning 
spiders,  of  the  wonderful  cave-dwellers,  and  of  the  cunning 
of  the  trap-door  spider. 


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